Objective optical system for an endoscope

ABSTRACT

An objective optical system is disclosed that is suitable for a high-precision endoscope that performs focusing by moving a single lens component. The objective optical system includes, in order from the object side, a front lens group, a middle lens group, and a rear lens group. The middle lens group is composed of two or more lens components, at least two of which have positive refractive power, and the lens component that is moved for focusing is in the middle lens group. Additionally, the objective optical system satisfies two specified conditions, and other conditions may apply.

This application claims benefit of foreign priority under 35 U.S.C. 119of Japanese Patent Application No. 2006-287437 filed on Oct. 23, 2006,the contents of which are hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a high image quality objective opticalsystem for an endoscope.

BACKGROUND OF THE INVENTION

In a so-called videoscope mounted with solid-state image pickup elementsat the tip of the insertion portion of an endoscope, a system foroutputting a high precision video signal of HDTV specification and/or PCformat has been commercialized. It is easy to realize a videoscope ofstandard specifications with pan focus if it has NTSC/PAL resolution.However, it becomes difficult to obtain a proper balance of opticalspecifications with pan focus due to effects of lowering sensitivitycaused by the reduction of pixels with solid-state image pickup elementsand deterioration of contrast caused by diffraction and other factors.Additionally, optical specifications when adopting progressive read-outtype, primary color, single-plate image pickup units or multi-plateimage pickup units, such as two-plate or three-plate units, whichprovide a high precision image other than by increasing the number ofpixels, are not established with pan focusing.

Therefore, in an objective optical system that provides high precisionimages, a decrease of f-number that is necessary to ensure a sufficientimage brightness for viewing a high precision image results in aninsufficient depth of field that must be compensated for by including afocusing function in the objective optical system.

The most general construction for providing the focusing function in anendoscope is a mount of the lens moving type. For a driving system inwhich lenses are moved by such a mount, a mount that can be arranged atthe tip of the endoscope in the vicinity of a moving lens is desirablefrom the viewpoint of power transmission efficiency and positionalaccuracy.

Objective optical systems described in the following cited referenceshave been known as prior art examples of objective optical systems foran endoscope having a focusing function by lens movement: JapanesePatent S55-15004; Japanese Patent H4-3851; Japanese Laid-Open PatentApplication H7-181377; Japanese Patent S55-15005; Japanese Laid-OpenPatent Application H11-316339; Japanese Laid-Open Patent Application2000-267002; Japanese Laid-Open Patent Application 2000-330015; JapaneseLaid-Open Patent Application 2002-28126; and Japanese Laid-Open PatentApplication 2002-357773.

In order to apply the optical systems described in these patentreferences to an endoscope with a focusing function havinghigh-precision solid-state image pickup elements, various problems mustbe addressed that will be discussed in the following comments.

However, first, definitions of the terms “lens element” and “lenscomponent,” that relate to the above cited patent references, as well asto the detailed description of the present invention that will followlater, will be given. The term “lens element” is herein defined as asingle transparent mass of refractive material having two opposedrefracting surfaces, which surfaces are positioned at least generallytransverse to the optical axis of the lens. The term “lens component” isherein defined as (a) a single lens element spaced so far from anyadjacent lens element that the spacing cannot be neglected in computingthe optical image forming properties of the lens elements or (b) two ormore lens elements that have their adjacent lens surfaces either in fulloverall contact or overall so close together that the spacings betweenadjacent lens surfaces of the different lens elements are so small thatthe spacings can be neglected in computing the optical image formingproperties of the two or more lens elements. Thus, some lens elementsmay also be lens components. Therefore, the terms “lens element” and“lens component” are not mutually exclusive terms. In fact, the termsmay frequently be used to describe a single lens element in accordancewith part (a) above of the definition of a “lens component.”Alternatively, a lens component may frequently be made by cementing lenselements together. Neither a filter with two flat faces nor a coverglass is a lens component.

In the above cited patent references, Japanese Patent S55-15004,Japanese Patent H4-3851, and Japanese Laid-Open Patent ApplicationH7-181377 relate to objective lenses for endoscopes, and in particularto embodiments where a moving lens group is composed of plural lenscomponents that are held in a frame. It is unavoidable that a movinglens group with a frame becomes long and heavy when the moving group iscomposed of plural lens components. This is undesirable because thetorque of an actuator for moving the moving lens group increases and theactuator becomes large in size. Embodiments described in the above citedJapanese Laid-Open Patent Application H11-316339 having a moving lensgroup of positive refractive power are also undesirable for the samereasons described above with regard to Japanese Patent S55-15004,Japanese Patent H4-3851, and Japanese Laid-Open Patent ApplicationH7-181377.

An embodiment of an objective lens for an endoscope described in theabove cited Japanese Patent S55-15005 is constructed for moving only onelens component, but the ray height on the first lens component is sohigh in this construction that the field of view angle cannot bewidened.

Embodiments having a moving lens group of negative refractive power havebeen described in the above cited Japanese Laid-Open Patent ApplicationH11-316339 and Japanese Laid-Open Patent Application 2000-267002. Inthese embodiments, the entire length of the optical systems is long andthe length of the rigid tip of the endoscope increases so that inendoscopes using such optical systems and that are capable of adjustmentto different viewing angles, operability related to such adjustmentsdeteriorates. Additionally, these optical systems are undesirable asoptical systems for endoscopes strictly in terms of focusingconsiderations because the fluctuations of focal length associated withthe lens movement are too large.

In embodiments of objective lenses for endoscopes described in the abovecited Japanese Laid-Open Patent Application 2000-330015 and embodimentsof an endoscope device described in the above cited Japanese Laid-OpenPatent Application 2002-28126, the moving lens component is on the imagemost side, and these embodiments are undesirable because of the largeoutside diameter of the lenses required, and the large size in theradial direction of any frame mounting such a large size lens that isused with any mechanism for moving such a lens.

An optical system for an endoscope has also been described in the abovecited Japanese Laid-Open Patent Application 2002-357773 with the lenscomponent on the image most side having negative refractive power. Thisoptical system is undesirable for use in combination with primary colorsingle plate image pickup elements or multiplate image pickup units,such as two-plate or three-plate units, because the exit pupil distanceis generally shortened.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to an objective optical system suitablefor a high precision endoscope having a focusing function by moving alens component, and particularly relates to an objective optical systemfor an endoscope suitable for mounting an actuator for lens movement atthe tip of the endoscope.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given below and the accompanying drawings, whichare given by way of illustration only and thus are not limitative of thepresent invention, wherein:

FIG. 1 is a cross-sectional view of Embodiment 1 of the presentinvention focused at the far point on the object side;

FIG. 2 is a cross-sectional view of Embodiment 2 of the presentinvention focused at the far point on the object side;

FIG. 3 is a cross-sectional view of Embodiment 3 of the presentinvention focused at the far point on the object side;

FIG. 4 is a cross-sectional view of Embodiment 4 of the presentinvention focused at the far point on the object side;

FIG. 5 is a cross-sectional view of Embodiment 5 of the presentinvention focused at the far point on the object side;

FIG. 6 is a cross-sectional view of Embodiment 6 of the presentinvention focused at the far point on the object side;

FIG. 7 is a cross-sectional view of Embodiment 7 of the presentinvention focused at the far point on the object side;

FIG. 8 is a cross-sectional view of Embodiment 8 of the presentinvention focused at the far point on the object side;

FIG. 9 is a cross-sectional view of Embodiment 9 of the presentinvention focused at the far point on the object side;

FIG. 10 is a cross-sectional view of Embodiment 10 of the presentinvention focused at the far point on the object side;

FIG. 11 is a cross-sectional view of Embodiment 11 of the presentinvention focused at the far point on the object side;

FIG. 12 is a cross-sectional view of Embodiment 12 of the presentinvention focused at the far point on the object side;

FIG. 13 is a cross-sectional view of Embodiment 13 of the presentinvention focused at the far point on the object side;

FIG. 14 is a cross-sectional view of Embodiment 14 of the presentinvention focused at the far point on the object side;

FIG. 15 is a cross-sectional view of Embodiment 15 of the presentinvention focused at the far point on the object side;

FIG. 16 is a cross-sectional view of Embodiment 16 of the presentinvention focused at the far point on the object side;

FIG. 17 is a cross-sectional view of Embodiment 17 of the presentinvention focused at the far point on the object side;

FIG. 18 is a cross-sectional view of Embodiment 18 of the presentinvention focused at the far point on the object side;

FIG. 19 is a cross-sectional view of Embodiment 19 of the presentinvention focused at the far point on the object side;

FIG. 20 is a cross-sectional view of Embodiment 20 of the presentinvention focused at the far point on the object side;

FIG. 21 is a cross-sectional view of Embodiment 21 of the presentinvention focused at the far point on the object side;

FIG. 22 is a cross-sectional view of Embodiment 22 of the presentinvention focused at the far point on the object side;

FIG. 23 is a cross-sectional view of Embodiment 23 of the presentinvention focused at the far point on the object side;

FIG. 24 is a cross-sectional view of Embodiment 24 of the presentinvention focused at the far point on the object side;

FIG. 25 is a cross-sectional view of Embodiment 25 of the presentinvention focused at the far point on the object side;

FIG. 26 is a cross-sectional view of Embodiment 26 of the presentinvention focused at the far point on the object side;

FIG. 27 is a cross-sectional view of Embodiment 27 of the presentinvention focused at the far point on the object side;

FIGS. 28A-28C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 1 of the present invention whenfocused at the far point on the object side, and FIGS. 28D-28F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 1 of the present invention when focused at the near point onthe object side;

FIGS. 29A-29C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 2 of the present invention whenfocused at the far point on the object side, and FIGS. 29D-29F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 2 of the present invention when focused at the near point onthe object side;

FIGS. 30A-30C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 3 of the present invention whenfocused at the far point on the object side, and FIGS. 30D-30F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 3 of the present invention when focused at the near point onthe object side;

FIGS. 31A-31C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 4 of the present invention whenfocused at the far point on the object side, and and FIGS. 31D-31F showthe spherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 4 of the present invention when focused at the near point onthe object side;

FIGS. 32A-32C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 5 of the present invention whenfocused at the far point on the object side, and FIGS. 32D-32F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 5 of the present invention focused at the near point on theobject side;

FIGS. 33A-33C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 6 of the present invention whenfocused at the far point on the object side, and FIGS. 33D-33F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 6 of the present invention when focused at the near point onthe object side;

FIGS. 34A-34C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 7 of the present invention whenfocused at the far point on the object side, and FIGS. 34D-34F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 7 of the present invention when focused at the near point onthe object side;

FIGS. 35A-35C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 8 of the present invention whenfocused at the far point on the object side, and FIGS. 35D-35F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 8 of the present invention when focused at the near point onthe object side;

FIGS. 36A-36C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 9 of the present invention whenfocused at the far point on the object side, and FIGS. 36D-36F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 9 of the present invention when focused at the near point onthe object side;

FIGS. 37A-37C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 10 of the present invention whenfocused at the far point on the object side, and FIGS. 37D-37F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 10 of the present invention when focused at the near point onthe object side;

FIGS. 38A-38C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 11 of the present invention whenfocused at the far point on the object side, and and FIGS. 38D-38F showthe spherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 11 of the present invention when focused at the near point onthe object side;

FIGS. 39A-39C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 12 of the present invention whenfocused at the far point on the object side, and FIGS. 39D-39F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 12 of the present invention when focused at the near point onthe object side;

FIGS. 40A-40C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 13 of the present invention whenfocused at the far point on the object side, and FIGS. 40D-40F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 13 of the present invention when focused at the near point onthe object side;

FIGS. 41A-41C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 14 of the present invention whenfocused at the far point on the object side, and FIGS. 41D-41F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 14 of the present invention when focused at the near point onthe object side;

FIGS. 42A-42C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 15 of the present invention whenfocused at the far point on the object side, and FIGS. 42D-42F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 15 of the present invention when focused at the near point onthe object side;

FIGS. 43A-43C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 16 of the present invention whenfocused at the far point on the object side, and FIGS. 43D-43F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 16 of the present invention when focused at the near point onthe object side;

FIGS. 44A-44C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 17 of the present invention whenfocused at the far point on the object side, and FIGS. 44D-44F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 17 of the present invention when focused at the near point onthe object side;

FIGS. 45A-45C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 18 of the present invention whenfocused at the far point on the object side, and FIGS. 45D-45F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 18 of the present invention when focused at the near point onthe object side;

FIGS. 46A-46C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 19 of the present invention whenfocused at the far point on the object side, and FIGS. 46D-46F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 19 of the present invention when focused at the near point onthe object side;

FIGS. 47A-47C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 20 of the present invention whenfocused at the far point on the object side, and FIGS. 47D-47F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 20 of the present invention when focused at the near point onthe object side;

FIGS. 48A-48C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 21 of the present invention whenfocused at the far point on the object side, and FIGS. 48D-48F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 21 of the present invention when focused at the near point onthe object side;

FIGS. 49A-49C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 22 of the present invention whenfocused at the far point on the object side, and FIGS. 49D-49F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 22 of the present invention when focused at the near point onthe object side;

FIGS. 50A-50C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 23 of the present invention whenfocused at the far point on the object side, and FIGS. 50D-50F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 23 of the present invention when focused at the near point onthe object side;

FIGS. 51A-51C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 24 of the present invention whenfocused at the far point on the object side, and FIGS. 51D-51F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 24 of the present invention when focused at the near point onthe object side;

FIGS. 52A-52C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 25 of the present invention whenfocused at the far point on the object side, and FIGS. 52D-52F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 25 of the present invention when focused at the near point onthe object side;

FIGS. 53A-53C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 26 of the present invention whenfocused at the far point on the object side, and FIGS. 53D-53F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 26 of the present invention when focused at the near point onthe object side; and

FIGS. 54A-54C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 27 of the present invention whenfocused at the far point on the object side, and FIGS. 54D-54F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 27 of the present invention when focused at the near point onthe object side.

DETAILED DESCRIPTION

In a first mode of construction of the present invention, an objectiveoptical system for an endoscope has an object side and an image side andincludes, arranged along an optical axis in order from the object side,as follows: a front lens group having negative refractive power andconsisting of a first lens component; a middle lens group havingpositive refractive power and including at least two lens components,each of said at least two lens components having positive refractivepower; and a rear lens group having positive refractive power andconsisting of only one lens component.

Additionally, only one lens component of said middle lens group moves inthe direction of the optical axis during focusing; a stop forcontrolling image brightness is positioned within the middle lens groupor between said front lens group and said middle lens group; and thefollowing conditions are satisfied:2<|f _(UM) /f _(TF)|<10  Condition (1)−1.25<f _(U1) /f _(TF)<−0.6  Condition (2)where

-   -   f_(UM) is the focal length of the only one lens component of the        middle lens group that moves for focusing;    -   f_(TF) is the focal length of the entire objective optical        system for an endoscope focused at the far point on the object        side; and    -   f_(U1) is the focal length of the first lens component of the        front lens group.

In the first mode of construction of the present invention as describedabove, the optical power arrangement is equivalent to a retrofocusoptical power arrangement of the front lens group, which is a singlelens component having negative refractive power, and the middle and rearlens groups having positive refractive power. This is a constructionsuited to an objective optical system for a high precision endoscopethat has high power and that has requirements of favorably correctedfield curvature. This construction is favorable for ensuring a largeenough back focal distance to allow for insertion of a filter, prism, orsimilar optical device on the image side of the optical system.

In this optical system, the first lens component that forms the frontlens group is stronger in refractive power relative to the other lenscomponents in order to provide for widening of the angle of view and tocorrect field curvature. Therefore, coefficients related to correctionof focusing and fluctuations in aberrations become large, making itdisadvantageous to make this first lens component be the lens group thatmoves for focusing. Additionally, the first lens component seals the tipof the endoscope, making it impossible for it to be the lens group thatmoves for focusing. The image-side lens component, that is the rear orimage-side lens group, has a principal ray height that is close to theimage height, thus requiring that the image-side lens component have alarge outside diameter. The middle lens group has a stop (either withinit, or on its object side) for controlling image brightness. Thisresults in a low principal ray height that allows lens elements of themiddle lens group to have smaller diameters than lens elements in theother lens groups of the objective optical system.

Constructing the optical system of the present invention with only onemoving lens group having the focusing function be the middle group andmade of lens elements of relatively small outside diameters enables themoving lens group to be small and light weight.

The rear or image-side lens group has positive refractive power andfunctions as a field lens, while the middle lens group functions mainlyas the lens group having positive refractive power of a retrofocus typeoptical system. This makes it possible for the middle lens group to havethe correction capability of a high precision optical system byconstructing the middle lens group with three or more lens components.

In order to reduce the occurrence of aberrations while ensuring anecessary positive refractive power of the middle lens group and reducethe sensitivity to manufacturing errors, it is preferable to make themiddle lens group with positive refractive power to include at least twolens components. Moreover, it is desirable to divide the optical powerin the middle lens group in order to control the optical power and thecorrection of the aberrations of the middle lens groups that moves forfocusing. Therefore, the lens components of the middle lens group thatrequire positive refractive power are at the object-side end and at theimage-side end of the middle lens group.

Additionally, the objective optical system satisfies Conditions (1) and(2) described above.

Condition (1) above assures the desired sensitivity of the focusingmovement of the moving lens component. In Condition (1), if the value of|f_(UM)/f_(TF)| is less than the lower limit value of two, the opticalpower of the moving lens component becomes too strong, and thefluctuations of focus associated with the movement of the moving lenscomponent become too large. This is undesirable because the movementrequired for focusing becomes very short and the required positionalaccuracy at the time of setting and maintaining the focus to apredetermined state increases. If the value of |f_(UM)/f_(TF)| isgreater than the upper limit value of ten of Condition (1), the opticalpower of the moving component becomes too weak, the movement requiredfor focusing increases, and the frame for holding the moving lenscomponent must be made longer.

Condition (2) above is provided to balance the outside diameter of thefirst lens component and the correction of field curvature. In Condition(2), if the value of f_(U1)/f_(TF) is less than the lower limit value of−1.25, this is undesirable because the negative refractive power of thefirst lens component becomes weaker and the outside diameter of thatlens component increases. If the value of f_(U1)/f_(TF) is more than theupper limit value of −0.6, this is undesirable because the negativerefractive power of the first lens component becomes too weak and thefield curvature tends to be overcorrected, the occurrence of astigmatismincreases with any eccentricity of the first lens component, andblurring of the image may easily occur.

In a second mode of construction of the present invention, an objectiveoptical system for an endoscope has an object side and an image side andincludes, arranged along an optical axis in order from the object side,as follows: a front lens group having negative refractive power andconsisting of a first lens component; a middle lens group havingpositive refractive power and consisting of, arranged in the followingorder from the object side, a second lens component having positiverefractive power, a third lens component, and a fourth lens componenthaving positive refractive power; and a rear lens group having positiverefractive power and consisting of a single lens component.Additionally, only one lens component in the middle lens group, that is,one of the second lens component, the third lens component, and thefourth lens component, as recited above, is moved in the direction ofthe optical axis in order to adjust focusing. Also, a stop forcontrolling image brightness is placed within the middle lens group orat the object end of the middle lens group. Furthermore, Conditions (1)and (2) set forth above are satisfied.

In the second mode of construction of the present invention, the middlelens group is constructed of three lens components. The second lenscomponent and the fourth lens component that are the lens components onthe object side and the image side, respectively, in the middle lensgroup have positive refractive power, as set forth above, and as alsoset forth in the first mode of construction of the present invention setforth above. The third lens component may have either positive ornegative refractive power.

Thus, the optical system can be made into a high precision objectiveoptical system with relatively few lens components as set forth abovewith regard to five lens components that are used.

In a third mode of construction of the present invention, an objectiveoptical system for an endoscope has an object side and an image side andincludes, arranged along an optical axis in order from the object side,as follows: a front lens group having negative refractive power andconsisting of a first lens component; a middle lens group havingpositive refractive power and consisting of, arranged in the followingorder from the object side, a second lens component having positiverefractive power, a third lens component, a fourth lens component, and afifth lens component having positive refractive power; and a rear lensgroup having positive refractive power and consisting of a single lenscomponent. Additionally, only one lens component in the middle lensgroup is moved in the direction of the optical axis in order to adjustfocusing. Also, a stop for controlling image brightness is placed withinthe middle lens group or at the object end of the middle lens group.Furthermore, Conditions (1) and (2) set forth above are satisfied.

In the third mode of construction of the present invention, the middlelens group is constructed with four lens components rather than threelens components, and lens components having positive refractive powerare arranged at both ends of the middle lens group. Namely, the secondlens component and the fifth lens component have positive refractivepower, and the third lens component and the fourth lens component may bemade to have either positive or negative refractive power.

In the third mode of construction of the present invention, anadditional degree of freedom in design is included by constructing theentire optical system with six lens components as compared to five lenscomponents as in the second mode of construction of the invention. Forexample, an expansion of the suitable range of various values of opticalsystem specifications and a reduction of distortion become possible.

In a fourth mode of construction of the present invention, an objectiveoptical system for an endoscope has an object side and an image side andincludes, arranged along an optical axis in order from the object side,as follows: a front lens group having negative refractive power andconsisting of a first lens component; a middle lens group havingpositive refractive power and consisting of, arranged in the followingorder from the object side, a second lens component having positiverefractive power, a stop for controlling image brightness, and a thirdlens component having positive refractive power; and a rear lens grouphaving positive refractive power and consisting of a single lenscomponent. Additionally, only one lens component in the middle lensgroup is moved in the direction of the optical axis in order to adjustfocusing. Furthermore, Conditions (1) and (2) set forth above aresatisfied.

In the fourth mode of construction of the present invention, the middlelens group consists of two lens components and the entire objectiveoptical system consists of four lens components. Although an objectiveoptical system for an endoscope of such an optical power arrangement hasbeen known, for example, in the above cited Japanese Laid-Open PatentApplication 2000-267002, such an optical system with favorably correctedaberrations that can correspond to high precision imaging may beachieved by satisfying Conditions (1) and (2) above. Therefore, theoptical system can also be adopted as an optical system that includesthe focusing function. In that case, having the last or image-side lenscomponent move to make focus adjustment, like the optical system shownin Japanese Laid-Open Patent Application 2000-267002, is undesirablebecause the outside diameter of the moving lens component increases.

In the fourth mode of construction of the optical system of the presentinvention, the outside diameter of the moving lens component can bedecreased by making either the second lens component or the third lenscomponent, both of which are in the middle lens group, the lenscomponent that moves for focusing.

In all of the first through fourth modes of construction of the presentinvention described above, any change in magnification due to focusingaction is preferably small. More specifically, the change is preferablywithin a range satisfying the following condition:0.85<f _(TN) /f _(TF)<1.15  Condition (3)where

-   -   f_(TN) is the focal length of the entire objective optical        system for an endoscope focused at the near point on the object        side; and    -   f_(TF) is defined as set forth above.

The optical system of the present invention does not use change of thefocal length in order to change the image size; rather, it is assumedthat image expansion (i.e., zooming) using electronics would be a betteralternative in order to vary the magnification of an observed image.Although optical expansion with less deterioration of image quality isgenerally desired, the more precise the image, the higher the spatialfrequency on the monitor screen and the more a deterioration of imagequality will occur when the spatial frequency on the monitor screen islowered using electronic expansion. Therefore, it is best thatelectronic expansion by an image processor be entirely relied upon forzooming since electronic expansion can achieve better balance relativeto the specifics of the uses and operation of an endoscope than whenusing an objective optical system having a zooming capability, sinceproviding such a capability for a high precision endoscope necessarilyresults in the endoscope becoming larger in size.

With the best use of electronic expansion, the more the input side ofimaging is limited in focusing, the more convenience of use is desired.In this regard, it is desirable that the change of optical magnificationwhen transitioning from the far point focused state to the near pointfocused state be limited to within 15%, as indicated by Condition (3)above in terms of the focal lengths at the near point focus and at thefar point focus.

Deviation of the optical system outside the range of Condition (3) aboveis undesirable because inconveniences otherwise occur too frequently,such as the viewing field being reduced too much in size that aparticular point of interest is no longer within the viewing field afterthe focus distance is adjusted, or the viewing field being expanded toomuch for clear viewing after the focus distance is adjusted. Theseproblems may require supplemental operations by the user, such aselectronically changing the magnification or making back and forthmovements with the inserted part in order to vary the field of view.Additionally, in the case of two step focus switching (or focusingswitching using additional steps), the fluctuation of magnificationassociated with the focus switching is divided and thus reduced, andthere will be no problem so long as Condition (3) above is satisfied foreach step. When an autofocus function is added, it is also useful tosatisfy Condition (3). Autofocus, once activated, operates independentlyof a user's intentions, and the image magnification can change greatlywith autofocusing. It is physically uncomfortable to view an image thatfluctuates in magnification. Fluctuations in magnification also affectthe autofocus mountings and movements. For example, the control of themoving direction and amount of movement during autofocus is usuallyderived from fluctuations of image contrast associated with very littlelens movement in a common focus detection mode. Fluctuations of imagemagnification affect the fluctuation of contrast, so a pure focusfluctuation component becomes difficult to detect and the accuracy ofthe autofocus control system deteriorates. Accordingly, when autofocusis utilized, it is desirable to satisfy Condition (3).

Regarding Condition (3), it is more preferable to set the upper limitvalue at unity in order to further limit the change of magnificationwith focus position, and thus it is further desirable that thefollowing, more narrow, condition be satisfied:0.85<f _(TN) /f _(TF)<1  Condition (4)where

-   -   f_(TN) and f_(TF) are defined as set forth above.

Condition (4) above assures a sufficient depth of field on the nearpoint side, as will now be discussed. The closer the near point side,the narrower the range of focal length and the wider the depth of fieldon the near point side. Manual focusing is associated with a reductionof image blur and image fluctuations because of a decrease of operatingfrequency of an actuator. The depth of field is inversely proportionalto the square of the focal length and is proportional to the f-number.Therefore, the shorter the focal length is, the greater the depth offield is (for a stop of constant size). Consequently, it is desirablethat focal lengths at the near point of focusing and at the far point offocusing be set up according to Condition (4). In other words, by havingthe value of the ratio f_(TN)/f_(TF) be unity or less, a sufficientdepth of field on the near point side can be provided.

Next, it is also desirable to satisfy the following conditions in theobjective optical systems for an endoscope of the present invention,with regard to all four modes of construction of the invention describedabove:n_(U1>)1.7  Condition (5)v_(U1)>38  Condition (6)where

-   -   n_(U1) is the refractive index at the d-line of the first lens        component of the front lens group; and    -   v_(U1) is the Abbe number at the d-line of the first lens        component of the front lens group.

As also mentioned in the description of the first mode of constructionof the present invention, in the objective optical system for anendoscope of the present invention, the first lens component of thefront lens group has relatively strong negative refractive power.Therefore, it would be undesirable for that first lens component to bemade as a cemented lens because that would tend to increase itsthickness and, as its thickness increases, the ray height rises and theoutside diameter increases. Therefore, a single lens element ispreferable and, in this case, the above Conditions (5) and (6) must besatisfied.

With regard to Condition (5), it would be undesirable if n_(U1), wereless than 1.7 because, as the radii of curvature of the lens elementsurfaces decrease, the workability of the lens element deteriorates, theeccentricity correction coefficient of astigmatism also deteriorates,the total thickness of the lens element becomes greater, and the rayheight increases.

With regard to Condition (6), it is undesirable that v_(U1) be less than38 because, in that case, large lateral color occurs in the first lenscomponent and an adverse effect on the aberration correction of theentire system is created.

It is desirable that the absolute values of the focal lengths of thelens components of the middle lens group and the rear lens group,designated as f_(U) (GM, GR), that is, the lens components other thanthe first lens group, be 1.4 f_(TF) or greater according to all fourmodes of construction of the optical system of the present inventiondescribed above.

When a high precision objective optical system is designed, theeccentricity correction coefficients for astigmatism, coma aberration,and spherical aberration must be controlled in relation to theaberrations. If the correction coefficients are large, the image qualityreadily deteriorates due to the inclination of the lens component in theframe.

The diameters of the lens elements are small, making it difficult tosuppress the eccentricity of lens components in the frames.

As described above, concentrating optical power in a specific lenscomponent with an extremely large eccentricity correction coefficientcan be avoided by making the absolute values of focal lengths of thelens components of the middle lens group and the rear lens group,designated as f_(U) (GM, GR), that is, the absolute values|f_(U)(GM,GR)|, to be 1.4 f_(TF) or greater.

If it is necessary for the absolute values of the focal lengths of theselens components to be less than 1.4 f_(TF), special considerationbecomes necessary so as to reduce the eccentricity of the lenscomponents in the frame, making it critical that the frame beconstructed with high accuracy.

It is also desirable that the absolute values of the radii of curvatureof the lens element surfaces of the lens components other than those inthe first lens group, designated |R(GM,GR)|, be 0.8 f_(TF) or greater inthe optical system of the present invention.

The conditions above concerning the focal lengths of the lens componentsother than those in the first lens group are based on considering theeccentricity correction coefficients, but the condition above concerningthe radii of curvature of these lens components, that is, the conditionrequiring their absolute values to be greater than 0.8 f_(TF), is acondition based on considering the eccentricity correction coefficientsof the lens element surfaces. If the eccentricity of the lens elementsurfaces, which are based on their outside diameters that relate toastigmatism, coma aberration, and spherical aberration, and the centraldeviation at cemented surfaces are large, the image quality readilydeteriorates. In order to improve the correction coefficients, it isnecessary not to decrease too much the absolute values of the radii ofcurvature of the lens element surfaces of the lens components. It wouldbe undesirable if the absolute values of the radii of curvature of thelens element surfaces become 0.8 f_(TF) or less because the centeringaccuracy and the cementing accuracy of the lens components must bestrict.

It is desirable that the last lens component that forms the rear lensgroup be a cemented lens component according to the first through fourthmodes of construction of the objective optical system for an endoscopeof the present invention as described above. It is desirable that thecemented lens be formed of a lens element having negative refractivepower with a refractive index (n_(d)) greater than 1.82 and an Abbenumber (v_(d)) of less than 26 and a lens element having positiverefractive power with a refractive index (n_(d)) of less than 1.78 andan Abbe number (v_(d)) greater than 49.

If the lens elements forming the last lens component do not satisfy theabove requirements, the lateral color and astigmatism (caused by theeffect of cementing together lens surfaces in a part where the principalray in the vicinity of the image side is high) will be excessive, makingaberration correction difficult.

Additionally, it is desirable that the last lens component satisfy thefollowing condition:2<f _(UR) /f _(TF)<12  Condition (7)where

-   -   f_(UR) is the focal length of the image-side lens component of        the rear lens group; and    -   f_(TF) is defined as set forth above.

The principal ray height is high in the image-side lens component of therear lens group. Therefore, that lens component acts as a field lenswith a role of controlling astigmatism and lateral color. On the otherhand, the middle lens group shares in the correction of sphericalaberration, coma aberration and axial chromatic aberration as describedabove.

Consequently, if the value of f_(UR)/f_(TF) is lower than the lowerlimit value of two, the image-side lens component of the rear lens grouphas a strong focusing action, excessively increasing problems ofspherical aberration and coma aberration so that aberration correctionof the optical system becomes difficult.

It is preferable to include in the objective optical system for anendoscope of the present invention, according to all of the firstthrough fourth modes of construction described above, two or morecemented lens components, each formed of a lens element having negativerefractive power and a lens element having positive refractive with thelens element having positive refractive power having a refractive indexat the d-line at least 0.1 less than that of the lens element havingnegative refractive power to which it is cemented.

In the optical system of the present invention, the Petzval sum mayeasily be a negative value because the first lens component has strongnegative refractive power, thus causing the field curvature to easily beovercorrected.

Therefore, it is effective to increase the degrees of freedom forcorrecting the Petzval sum toward positive values by increasing the useof cemented lens components formed of a lens element having negativerefractive power and a relatively high refractive index cemented to alens element having positive refractive power and a relatively lowrefractive index. The Petzval sum becomes a design restriction beforeother aberration corrections because it is determined only by opticalpower arrangements and refractive indices. Therefore, it is undesirablefor the above design criteria not to be satisfied, because that woulddecrease the feasibility of aberration correction.

In the optical system of the present invention, it is desirable that thelens component arranged in the middle lens group and that is moved forfocusing have positive refractive power from a viewpoint of efficiencyof optical power arrangements, including the middle lens group havingpositive refractive power as a whole. When the moving lens component isformed as a single lens element having positive refractive power, it ismore preferable that the refractive index n_(d) at the d-line be lessthan 1.75. If the correction of field curvature with cemented lenscomponents as set forth above is also considered, it is preferable thatthe single lens element having positive refractive power have a lowerrefractive index in order to make it easy to correct the Petzval sum inthe positive direction. In embodiments of the present invention, it isdesirable to make the moving lens component to be a single lens elementhaving positive refractive power and to use material with a lowrefractive index so as to enhance the capability of making desiredphysical shapes of the lens element because the Z coefficient can beincreased. It would be undesirable to have the refractive index of thelens element be above 1.75 because the degree of freedom for design ofthe optical system would be reduced due to restrictions on the opticalpower arrangement, field curvature would tend to be excessive, and itwould be more difficult to ensure accuracy of the Z coefficient.

In the optical system of the present invention, it is preferable to usea cemented lens component having positive refractive power as the movinglens component because the restriction of the Z coefficient in the caseof a positive single lens is eliminated. When the moving lens componentis constructed as a positive cemented lens, it is preferable to cement alens element having negative refractive power and a lens element havingpositive refractive with a refractive index at the d-line at least 0.1less than that of the lens element having negative refractive power towhich it is cemented. This combination relaxes restrictions on designrelated to the Petzval sum, as described above. It would be undesirableif this design criterion was not satisfied, as failing to satisfy thisdesign criterion would reduce the feasibility of aberration correction.

It is desirable, as described above, that the lens component moved forfocusing be adjacent to a stop for controlling image brightness. Themoving lens component adjacent to the brightness stop has the lowestprincipal ray height in the middle lens group. Therefore, if the lenscomponent adjacent to the brightness stop is the lens component movedfor focusing, the outside diameter of that lens component can bereduced. It would be undesirable if this design criterion were notsatisfied, because then the lens component moved for focusing would tendto become larger and heavier.

The fourth mode of construction of the present invention, describedabove, wherein the middle lens group consists of a second lens componentand a third lens component with a brightness stop between them andeither lens component of the middle lens group is moved for focusing maybe implemented to also satisfy the requirements described above.

When the middle lens group includes more than two lens components, it isdesirable that the lens component moved for focusing be a lens componentthat is not at either end of the middle lens group. The lens componentmoved for focusing is positioned near the center of the entire objectiveoptical system. In a retrofocus type objective optical system, thecenter position is a place where an axial beam is close to a relativelya focal beam and fluctuation of axial aberrations, spherical aberrationand axial chromatic aberration associated with the movement of thefocusing lens component is easily reduced, making it possible toemphasize correction of off-axis aberrations, astigmatism and lateralcolor, that fluctuate with movement of the focusing lens component,thereby reducing restrictions on the design for aberration correction.If the above design criterion is not satisfied, this is undesirablebecause the aberration fluctuation associated with the movementincreases.

In the first mode of construction of the objective optical system for anendoscope of the present invention, the middle lens group is formed oftwo or more lens components, and one or more of these lens componentssatisfy the above criteria. In the second mode of construction of theobjective optical system for an endoscope of the present invention, themiddle lens group consists of only three lens components. In the thirdmode of construction, the third and the fourth lens components satisfythe above criteria. In the fourth mode of construction of the objectiveoptical system for an endoscope of the present invention, the threedesign criteria described above are not required, but these designcriteria relate to the lens being moved for focusing being limited toone of the second and third lens components.

As described above, it is variously preferable that the lens componentmoved for focusing not be at either end of the middle lens group andthat the lens component moved for focusing be adjacent the stop forcontrolling image brightness and have a positive refractive power as setforth above with regard to the first through third modes of constructionof the present invention.

An actuator for driving the lens component that moves for focusing issmall in the radial direction of the insertion part of the endoscope,and an electronically controllable actuator is desirable. A shape memoryalloy actuator is considered as an exemplary choice for the actuator. Itis known that if a voltage is applied to a wire formed of a shape memoryalloy material such as titanium nickel, a force is produced when thewire is heated to a high temperature by electric resistance, andcontraction in the longitudinal direction is great. The alloy materialscan be used not only in the form of wire but also in the form of coils.The length of wire and/or coils of the shape memory alloys can bechanged by temperature controlled through an applied voltage.

An objective optical system for an endoscope of the present inventionhas a wide field angle, has good correction of various aberrations,including curvature of field, and provides for focus adjustment withmovement of a lens component having a small diameter and a small size,proper sensitivity throughout the range of movement for focusing, andlittle fluctuation in image quality throughout the range of movement forfocusing.

Embodiments 1 through 27 of the objective optical system for anendoscope of the present invention will now be individually describedwith further reference to the drawings. In all of Embodiments 1 through27, the data of the objective optical system of each embodiment is shownin a corresponding table. At the top of each of these tables are listedvalues of the working distance WD (in mm) for the far point focusedstate and the near point focused state as well as the focal length (inmm), the f-number (i.e., F_(NO)), and the field angle 2ω (in degrees) atboth the far point focused state (focal length f_(TF)) and near pointfocused state (focal length f_(TN)). Below that in each table are listedfor each optical surface, as numbered from the object side through theuse of subscripts, the radius of curvature r (in mm) on the optical axisof each optical surface, the on-axis surface spacing d (in mm) at thefar point focused state, as well as the refractive index n and the Abbenumber v (both as measured at the d-line wavelength of 587.6 nm) for thematerial on the image side of the optical surface. Below that in eachtable are listed the values |f_(UM)/f_(TF)|, f_(U1)/f_(TF), andf_(TN)/f_(TF), related to the above Conditions (1), (2) and (3)-(4),respectively. Below that in each table are listed the focal lengths ofthe lens components in order from the object side (left column), as wellas the ratio of these focal lengths to f_(TF) (right column). Below thatin each table are listed the minimum value of the absolute values of thefocal lengths of the lens components of each of the middle lens groupand lens components of the rear or image-side lens group,|f_(U)(GM,GR)|_(min) and the minimum value of the absolute values of theradii of curvature of the lens elements of the lens components of themiddle lens group and the lens elements of the lens components of therear or image-side lens group, |R(GM,GR)|_(min). Below that in eachtable, except in the tables of Embodiments 6 and 26, are listed for therear or image-side lens group (that consists of a cemented lenscomponent formed of a lens element having negative refractive power anda lens element having positive refractive power) the refractive index ofthe lens element having positive refractive power, the refractive indexof the lens element having negative refractive power, as well as theAbbe number of the lens element having positive refractive power and theAbbe number of the lens element having negative refractive power, allvalues being measured at the d-line wavelength of 587.6 nm. For eachembodiment, figures are provided that show the spherical aberration (inmm), the astigmatism (in mm) in both the sagittal (S) and meridional (M)image planes, and the distortion (in %), as discussed further below.

EMBODIMENT 1

FIG. 1 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 1 of the present invention. In FIG. 1, aswell as in FIGS. 2-26, IP is the image plane. Table 1 below lists thevarious data explained above for Embodiment 1.

TABLE 1 Far point focused state WD = 48 f_(TF) = 1.790 F_(NO) = 4.48 2 ω= 98.6° Near point focused state WD = 23 f_(TN) = 1.758 F_(NO) = 4.48 2ω = 100.9° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.4291 d₂ =0.6995 r₃ = −6.9299 d₃ = 0.5800 n₂ = 1.72916 ν₂ = 54.68 r₄ = −2.5937 d₄= 0.6725 r₅ = ∞ (stop) d₅ = 1.0825 r₆ = −4.1260 d₆ = 0.6000 n₃ = 1.72916ν₃ = 54.68 r₇ = −2.6280 d₇ = 0.1000 r₈ = −6.3523 d₈ = 0.6000 n₄ =1.80610 ν₄ = 40.92 r₉ = −3.0721 d₉ = 0.1000 r₁₀ = ∞ d₁₀ = 0.4500 n₅ =1.51800 ν₅ = 75.00 r₁₁ = ∞ d₁₁ = 0.1000 r₁₂ = 5.1077 d₁₂ = 1.1000 n₆ =1.58913 ν₆ = 61.14 r₁₃ = −2.7000 d₁₃ = 0.3000 n₇ = 1.92286 ν₇ = 18.90r₁₄ = −8.6620 d₁₄ = 0.6000 r₁₅ = ∞ d₁₅ = 3.6000 n₈ = 1.48749 ν₈ = 70.23r₁₆ = ∞ (image plane) |f_(UM)/f_(TF)| = 3.006 f_(U1)/f_(TF) = −1.039f_(TN)/f_(TF) = 0.982 f_(U1) = −1.860 f_(U1)/f_(TF) = −1.04 f_(U2) =5.381 f_(U2)/f_(TF) = 3.01 f_(U3) = 8.493 f_(U3)/f_(TF) = 4.75 f_(U4) =6.823 f_(U4)/f_(TF) = 3.81 f_(UR) = 10.039 f_(UR)/f_(TF) = 5.61 |f_(U)(GM, GR)|_(min) = 3.01 |R (GM, GR)|_(min) = 1.45 n(GR_(p)) = n₆ =1.58913 n(GR_(n)) = n₇ = 1.92286 ν(GR_(p)) = ν₆ = 61.14 ν(GR_(n)) = ν₇ =18.90

The optical system of Embodiment 1, as shown in FIG. 1, is composed of:a front lens group that consists of a lens component that has negativerefractive power and is formed of a single lens element with lenssurfaces having radii of curvature r₁ and r₂; a middle lens group thatconsists of three lens components that are all single lens elementshaving positive refractive power, specifically, a second lens elementhaving radii of curvature r₃ and r₄, a third lens element having radiiof curvature r₆ and r₇, and a fourth lens element having radii ofcurvature r₈ and r₉; and a rear lens group that consists of a cementedlens component made up of a biconvex lens element and a meniscus lenselement having negative refractive power with radii of curvature r₁₂,r₁₃, and r₁₄.

Embodiment 1 is an example of an optical system according to the firstand second modes of construction of the present invention describedabove with regard to the middle lens group, referenced by “GM” in Table1 above and in FIG. 1, being composed of three lens components, namely,a second lens component having positive refractive power, a third lenscomponent, and a fourth lens component, in order from the object side.

A stop S for controlling image brightness and having a radius ofcurvature r₅ is arranged between the second lens component and the thirdlens component in the middle lens group at a position having arelatively low ray height. The second lens component moves toward theimage side during focusing from the far point to the near point asindicated by the directional arrow in FIG. 1 over a range indicated bythe data of Table 1 above. This second lens component is a single lenselement, has a relatively small diameter and is relatively thin, and ismade with a supporting frame capable of being of small size andlightweight and thus suitable for being easily moved. The first lenscomponent is a plano-concave lens element made of highly durablesapphire (n_(d)=1.76820, v_(d)=71.79) and protects the object-sidesurface. A plane parallel plate F with radii of curvature r₁₀ and r₁₁ isarranged between the fourth lens component and the last lens group andoperates as an absorption infrared cutoff filter (n_(d)=1.5180,v_(d)=75.00) on which a laser reflecting film may be deposited asnecessary for the design. A cemented lens component is used for the lastlens component in order to correct astigmatism and lateral color. Aglass block B, having radii of curvature r₁₅ and r₁₆ is arranged on theimage-most side or in simpler designs may be replaced by single-plate,solid-state image pickup elements. Alternatively, the optical axis maybe folded 90° using an optical path conversion prism, and single-plateimage pickup elements may be placed horizontally or a multi-plate (e.g.,two-plate) image pickup unit may be used.

Embodiment 1 of the present invention satisfies Conditions (1) through(7) above. The focal lengths f_(U)(GM,GR) of the lens components in themiddle lens group and rear lens group and the radii of curvatureR(GM,GR) of lens surfaces of the lens components in the middle lensgroup and rear lens group also satisfy the applicable conditions anddesign criteria as specified for them. As described above, the last lenscomponent is a cemented lens component, and the refractive indicesn(GR_(p)) and n(GR_(n)) and the Abbe numbers v(GR_(p)) and v(GR_(n)) ofthe lens materials of this lens component also satisfy the applicableconditions and design criteria of the present invention.

FIGS. 28A-28C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 1 of the present invention whenfocused at the far point on the object side, and FIGS. 28D-28F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 1 of the present invention when focused at the near point onthe object side. As shown in FIGS. 28A-28C and FIGS. 28D-28F, inEmbodiment 1 these aberrations are favorably corrected.

EMBODIMENT 2

FIG. 2 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 2 of the present invention. Table 2 belowlists the various data explained above for Embodiment 2.

TABLE 2 Far point focused state WD = 47 f_(TF) = 1.800 F_(NO) = 4.52 2 ω= 98.6° Near point focused state WD = 23 f_(TN) = 1.765 F_(NO) = 4.55 2ω = 100.9° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.4200 d₂ =1.0546 r₃ = −11.8050 d₃ = 0.6000 n₂ = 1.80100 ν₂ = 34.97 r₄ = −2.8044 d₄= 0.3904 r₅ = ∞ (stop) d₅ = 1.0008 r₆ = −5.1964 d₆ = 0.3000 n₃ = 1.80518ν₃ = 25.42 r₇ = 16.3100 d₇ = 0.7500 n₄ = 1.51742 ν₄ = 52.43 r₈ = −2.7213d₈ = 0.1000 r₉ = −30.4133 d₉ = 0.6500 n₅ = 1.83481 ν₅ = 42.71 r₁₀ =−3.6000 d₁₀ = 0.1000 r₁₁ = ∞ d₁₁ = 0.4500 n₆ = 1.51800 ν₆ = 75.00 r₁₂ =∞ d₁₂ = 0.1000 r₁₃ = 6.2138 d₁₃ = 1.0000 n₇ = 1.58913 ν₇ = 61.14 r₁₄ =−2.8000 d₁₄ = 0.3000 n₈ = 1.84666 ν₈ = 23.78 r₁₅ = −17.3297 d₁₅ = 0.6000r₁₆ = ∞ d₁₆ = 3.6000 n₉ = 1.48749 ν₉ = 70.23 r₁₇ = ∞ (image plane)|f_(UM)/f_(TF)| = 2.478 f_(U1)/f_(TF) = −1.027 f_(TN)/f_(TF) = 0.981f_(U1) = −1.848 f_(U1)/f_(TF) = −1.03 f_(U2) = 4.460 f_(U2)/f_(TF) =2.48 f_(U3) = 26.144 f_(U3)/f_(TF) = 14.52 f_(U4) = 4.838 f_(U4)/f_(TF)= 2.69 f_(UR) = 18.451 f_(UR)/f_(TF) = 10.25 |f_(U) (GM, GR)|_(min) =2.48 |R (GM, GR)|_(min) = 1.51 n(GR_(p)) = n₇ = 1.58913 n(GR_(n)) = n₈ =1.84666 ν(GR_(p)) = ν₇ = 61.14 ν(GR_(n)) = ν₈ = 23.78

The optical system of Embodiment 2, as shown in FIG. 2, is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₁ and r₂; a middle lens groupthat consists of three lens components, namely, a second lens componentthat is formed as a single lens element having radii of curvature r₃ andr₄, a cemented third lens component made up of a biconcave lens elementcemented to a biconvex lens element with radii of curvature r₆, r₇, andr₈, and a fourth lens component that is formed as a single lens elementhaving positive refractive power and radii of curvature r₉ and r₁₀; anda rear lens group that consists of a cemented lens component made up ofa biconvex lens element cemented to a meniscus lens element havingnegative refractive power with radii of curvature r₁₃, r₁₄, and r₁₅.

Embodiment 2 is also an example of an optical system according to thefirst and second modes of construction of the present inventiondescribed above with regard to the middle lens group, referenced by “GM”in Table 2 above and in FIG. 2, being composed of three lens components,namely, a second lens component having positive refractive power, athird lens component, and a fourth lens component having positiverefractive power, in order from the object side. A stop S forcontrolling image brightness and having a radius of curvature r₅ isarranged between the second lens component and the third lens componentin the middle lens group. A plane parallel plate F with radii ofcurvature r₁₁ and r₁₂ is arranged between the fourth lens component andthe rear lens group and operates as an absorption infrared cutofffilter, and a glass block B, having radii of curvature r₁₆ and r₁₇, isarranged on the image-most side of the optical system.

Embodiment 2 is different from Embodiment 1 in that the stop S thatcontrols image brightness is moved integrally with the lens componentthat moves for focusing and in that the third lens component is acemented lens. Other features of Embodiment 2 are very similar toEmbodiment 1. When the stop S that controls image brightness moves alongwith the lens component that moves for focusing, the f-number and theposition of the exit pupil change, but these changes are slight in theoptical system of Embodiment 2. Whether the stop controlling imagebrightness is moved integrally with the lens component that moves forfocusing may be decided by considerations of the preferred framestructures for mounting the particular optical elements. Theseconsiderations may be applied to the other disclosed embodiments of thepresent invention in determining the applicability of moving the stopwith the lens component moved for focusing.

In Embodiment 2, as described above, the third lens component is formedas a cemented lens component and the control of axial chromaticaberration and spherical aberration is easily performed. Therefore, theaberration correction associated with a lens surface of small curvaturemay not create a problem, and the fluctuations in aberrations due toeccentricity of a lens surface can be reduced. The meniscus shape of themeniscus lens element also does not have to be so pronounced, thusimproving the workability of lens elements used.

In Embodiment 2, the field curvature readily tends to be overcorrecteddue to a strong negative refractive power of the first lens component,but the correction of curvature of field is easily made by adding acemented lens component formed of a lens having positive refractivepower and a low refractive index with a lens element having negativerefractive power and a high refractive index.

Embodiment 2 of the present invention, just as with Embodiment 1,satisfies Conditions (1) through (7) above. The focal lengthsf_(U)(GM,GR) of the lens components in the middle lens group and rearlens group and the radii of curvature R(GM,GR) of the lens surfaces ofthe lens components in the middle lens group and rear lens group alsosatisfy the applicable conditions and design criteria as specified forthem. As described above, the refractive indices n(GR_(p)) and n(GR_(n))and the Abbe numbers v(GR_(p)) and v(GR_(n)) of the lens materials ofthe cemented lens component that is the last lens component of the rearlens group also satisfy the applicable conditions and design criteria ofthe present invention.

FIGS. 29A-29C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 2 of the present invention whenfocused at the far point on the object side, and FIGS. 29D-29F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 2 of the present invention when focused at the near point onthe object side. As shown in FIGS. 29A-29C and FIGS. 29D-29F, inEmbodiment 2 these aberrations are favorably corrected.

EMBODIMENT 3

FIG. 3 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 3 of the present invention. Table 3 belowlists the various data explained above for Embodiment 3.

TABLE 3 Far point focused state WD = 46 f_(TF) = 1.845 F_(NO) = 4.46 2 ω= 98.6° Near point focused state WD = 23 f_(TN) = 1.789 F_(NO) = 4.35 2ω = 102.6° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.3633 d₂ =0.5500 r₃ = 9.9958 d₃ = 1.6230 n₂ = 1.80100 ν₂ = 34.97 r₄ = −3.4155(stop) d₄ = 0.5076 r₅ = −6.3158 d₅ = 0.3000 n₃ = 1.88300 ν₃ = 40.76 r₆ =13.0944 d₆ = 0.5000 r₇ = −8.2243 d₇ = 0.7000 n₄ = 1.72916 ν₄ = 54.68 r₈= −2.2479 d₈ = 0.1000 r₉ = 6.1134 d₉ = 1.2000 n₅ = 1.72916 ν₅ = 54.68r₁₀ = −2.7228 d₁₀ = 0.3000 n₆ = 1.92286 ν₆ = 18.90 r₁₁ = −6.2637 d₁₁ =0.1000 r₁₂ = ∞ d₁₂ = 0.4500 n₇ = 1.51800 ν₇ = 75.00 r₁₃ = ∞ d₁₃ = 0.8000r₁₄ = ∞ d₁₄ = 3.6000 n₈ = 1.48749 ν₈ = 70.23 r₁₅ = ∞ (image plane)|f_(UM)/f_(TF)| = 2.597 f_(U1)/f_(TF) = −0.962 f_(TN)/f_(TF) = 0.970f_(U1) = −1.775 f_(U1)/f_(TF) = −0.96 f_(U2) = 3.359 f_(U2)/f_(TF) =1.82 f_(U3) = −4.791 f_(U3)/f_(TF) = −2.60 f_(U4) = 4.043 f_(U4)/f_(TF)= 2.19 f_(UR) = 5.321 f_(UR)/f_(TF) = 2.88 |f_(U) (GM, GR)|_(min) = 1.82|R (GM, GR)|_(min) = 1.22 n(GR_(p)) = n₅ = 1.72916 n(GR_(n)) = n₆ =1.92286 ν(GR_(p)) = ν₅ = 54.68 ν(GR_(n)) = ν₆ = 18.90

As shown in FIG. 3, the optical system of Embodiment 3 is composed of: afront lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₁ and r₂; a middle lens groupthat consists of three lens components, specifically, a biconvex secondlens element having radii of curvature r₃ and r₄, a biconcave third lenselement having radii of curvature r₅ and r₆, and a fourth lens elementhaving positive refractive power and a meniscus shape and radii ofcurvature r₇ and r₈; and a rear lens group that consists of a cementedlens component made up of a biconvex lens element and a meniscus lenselement having negative refractive power with radii of curvature r₉,r₁₀, and r₁₁.

Embodiment 3 is an example of an optical system according to the firstand second modes of construction of the present invention describedabove with regard to the middle lens group, referenced by “GM” in Table3 above and in FIG. 3, that is composed of three lens components,namely, a second lens component having positive refractive power, athird lens component, and a fourth lens component having positiverefractive power, in order from the object side.

In Embodiment 3, the third lens component, which is the lens componenthaving negative refractive power in the middle lens group, is the lenscomponent that moves for focusing. This moving lens component is movedtoward the object side during focusing from the far point to the nearpoint. Because the third lens component has negative refractive power,the positive refractive power in the area immediately on the image sideof that third lens component tends to be insufficient. Therefore, theimage-side lens component of the rear lens group is arranged on theobject side of the plane parallel plate F with radii of curvature r₁₂and r₁₃ in order to compensate for that optical power deficiency. Thestop for controlling image brightness is positioned on the image-sidelens surface of the second lens component.

In Embodiment 3, the design of the optical system according to thesecond mode of construction of the present invention is possible even ifthe third lens component is constructed so as to have negativerefractive power and, in practice, sufficient aberration correction canbe achieved even when the lens component having negative refractivepower is moved for focusing.

Embodiment 3 of the present invention also satisfies Conditions (1)through (7) above, as shown by Table 3 above. The focal lengthsf_(U)(GM,GR) of the lens components in the middle lens group and rearlens group and the radii of curvature R(GM,GR) of the lens elementsurfaces of the lens components in the middle lens group and rear lensgroup also satisfy the applicable conditions and design criteriaspecified for them. As described above, the refractive indices n(GR_(p))and n(GR_(n)) and the Abbe numbers v(GR_(p)) and v(GR_(n)) of the lensmaterials of the cemented lens component that is the last lens componentof the rear lens group also satisfy the applicable conditions and designcriteria of the present invention.

FIGS. 30A-30C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 3 of the present invention whenfocused at the far point on the object side, and FIGS. 30D-30F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 3 of the present invention when focused at the near point onthe object side. As shown in FIGS. 30A-30C and FIGS. 30D-30F, inEmbodiment 3 these aberrations are favorably corrected.

EMBODIMENT 4

FIG. 4 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 4 of the present invention. Table 4 belowlists the various data explained above for Embodiment 4.

TABLE 4 Far point focused state WD = 46 f_(TF) = 1.830 F_(NO) = 4.50 2 ω= 98.6° Near point focused state WD = 23 f_(TN) = 1.736 F_(NO) = 4.28 2ω = 104.7° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.2738 d₂ =0.5500 r₃ = 11.1859 d₃ = 1.8838 n₂ = 1.80100 ν₂ = 34.97 r₄ =−2.5133(stop) d₄ = 0.3000 r₅ = −6.3316 d₅ = 0.3000 n₃ = 1.88300 ν₃ =40.76 r₆ = 8.3186 d₆ = 0.5000 r₇ = −9.4262 d₇ = 0.7000 n₄ = 1.72916 ν₄ =54.68 r₈ = −2.3327 d₈ = 0.5713 r₉ = 14.3039 d₉ = 1.2000 n₅ = 1.72916 ν₅= 54.68 r₁₀ = −2.3012 d₁₀ = 0.3000 n₆ = 1.92286 ν₆ = 18.90 r₁₁ = −4.2482d₁₁ = 0.1000 r₁₂ = ∞ d₁₂ = 0.4500 n₇ = 1.51800 ν₇ = 75.00 r₁₃ = ∞ d₁₃ =0.8000 r₁₄ = ∞ d₁₄ = 3.6000 n₈ = 1.48749 ν₈ = 70.23 r₁₅ = ∞ (imageplane) |f_(UM)/f_(TF)| = 2.230 f_(U1)/f_(TF) = −0.906 f_(TN)/f_(TF) =0.949 f_(U1) = −1.658 f_(U1)/f_(TF) = −0.91 f_(U2) = 2.729 f_(U2)/f_(TF)= 1.49 f_(U3) = −4.033 f_(U3)/f_(TF) = −2.20 f_(U4) = 4.081f_(U4)/f_(TF) = 2.23 f_(UR) = 5.545 f_(UR)/f_(TF) = 3.03 |f_(U) (GMGR)|_(min) = 1.49 |R (GM, GR)|_(min) = 1.26 n(GR_(p)) = n₅ = 1.72916n(GR_(n)) = n₆ = 1.92286 ν(GR_(p)) = ν₅ = 54.68 ν(GR_(n)) = ν₆ = 18.90

As shown in FIG. 4, the optical system of Embodiment 4 is composed of: afront lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₁ and r₂; a middle lens groupthat consists of three lens components, specifically, a second lenselement having positive refractive power and radii of curvature r₃ andr₄, a third lens element having negative refractive power and radii ofcurvature r₅ and r₆, and a fourth lens element having positiverefractive power and radii of curvature r₇ and r₈; a rear lens groupthat consists of a cemented lens component made up of a biconvex lenselement cemented to a meniscus lens element having negative refractivepower with radii of curvature r₉, r₁₀, and r₁₁; an infrared cutofffilter F with radii of curvature r₁₂ and r₁₃; and a glass block B,having radii of curvature r₁₄ and r₁₅, that is arranged on theimage-most side of the optical system.

Embodiment 4 is an example of an optical system according to the firstand second modes of construction of the present invention describedabove in which the third lens component in the middle lens group,referenced by “GM” in Table 4 above and in FIG. 4, has negativerefractive power. Embodiment 4 is different from Embodiment 3 in thatthe fourth lens component having positive refractive power is the lenscomponent that is moved for focusing. Thus, if the middle lens grouphaving this basic optical power arrangement is constructed to haveaberration correcting ability, the optical system of the presentinvention can be simply realized by ensuring a space for movement of themoving lens component even if the fourth lens component is the movinglens component, as in Embodiment 4. In Embodiment 4, the fourth lenscomponent is moved toward the image side during focusing from the farpoint to the near point on the object side.

Embodiment 4 of the present invention also satisfies Conditions (1)through (7) above, as shown by Table 4 above. The focal lengthsf_(U)(GM,GR) of the lens components in the middle lens group and rearlens group and the radii of curvature R(GM,GR) of the lens surfaces ofthe lens components in the middle lens group and rear lens group alsosatisfy the applicable conditions and design criteria specified forthem. As described above, the refractive indices n(GR_(p)) and n(GR_(n))and the Abbe numbers v(GR_(p)) and v(GR_(n)) of the lens materials ofthe cemented lens component that is the last lens component of the rearlens group also satisfy the applicable conditions and design criteria ofthe present invention.

FIGS. 31A-31C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 4 of the present invention whenfocused at the far point on the object side, and FIGS. 31D-31F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 4 of the present invention when focused at the near point onthe object side. As shown in FIGS. 31A-31C and FIGS. 31D-31F, inEmbodiment 4 these aberrations are favorably corrected.

EMBODIMENT 5

FIG. 5 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 5 of the present invention. Table 5 belowlists the various data explained above for Embodiment 5.

TABLE 5 Far point focused state WD = 46 f_(TF) = 1.820 F_(NO) = 4.50 2 ω= 98.6° Near point focused state WD = 23 f_(TN) = 1.757 F_(NO) = 4.37 2ω = 101.8° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.3763 d₂ =0.7000 r₃ = −4.9953 d₃ = 0.5380 n₂ = 1.75500 ν₂ = 52.32 r₄ = −2.6223 d₄= 0.6894 r₅ = ∞ (stop) d₅ = 0.9027 r₆ = −5.3414 d₆ = 0.5000 n₃ = 1.48749ν₃ = 70.23 r₇ = −2.4247 d₇ = 0.7196 r₈ = −18.7123 d₈ = 0.6000 n₄ =1.88300 ν₄ = 40.76 r₉ = −3.7651 d₉ = 0.1009 r₁₀ = ∞ d₁₀ = 0.4500 n₅ =1.51800 ν₅ = 75.00 r₁₁ = ∞ d₁₁ = 0.1000 r₁₂ = 5.2090 d₁₂ = 1.1000 n₆ =1.58913 ν₆ = 61.14 r₁₃ = −3.000 d₁₃ = 0.3000 n₇ = 1.92286 ν₇ = 18.90 r₁₄= −16.4746 d₁₄ = 0.6000 r₁₅ = ∞ d₁₅ = 3.6000 n₈ = 1.48749 ν₈ = 70.23 r₁₆= ∞ (image plane) |f_(UM)/f_(TF)| = 4.738 f_(U1)/f_(TF) = −0.985f_(TN)/f_(TF) = 0.965 f_(U1) = −1.792 f_(U1)/f_(TF) = −0.98 f_(U2) =6.662 f_(U2)/f_(TF) = 3.66 f_(U3) = 8.624 f_(U3)/f_(TF) = 4.74 f_(U4) =5.239 f_(U4)/f_(TF) = 2.88 f_(UR) = 16.102 f_(UR)/f_(TF) = 8.85 |f_(U)(GM, GR)|_(min) = 2.88 |R (GM, GR)|_(min) = 1.33 n(GR_(p)) = n₆ =1.58913 n(GR_(n)) = n₇ = 1.92286 ν(GR_(p)) = ν₆ = 61.14 ν(GR_(n)) = ν₇ =18.90

The optical system of Embodiment 5, as shown in FIG. 5, is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₁ and r₂; a middle lens groupthat consists of three lens components that are all single lens elementshaving positive refractive power, specifically, a second lens elementhaving radii of curvature r₃ and r₄, a third lens element having radiiof curvature r₆ and r₇, and a fourth lens element having radii ofcurvature r₈ and r₉; and a rear lens group that consists of a cementedlens component made up of a biconvex lens element cemented to a meniscuslens element having negative refractive power with radii of curvaturer₁₂, r₁₃, and r₁₄.

Embodiment 5 is an example of an optical system according to the firstand second modes of construction of the present invention describedabove with regard to the middle lens group, referenced by “GM” in Table5 above and in FIG. 5, which is composed of three lens components,namely, a second lens component having positive refractive power, athird lens component, and a fourth lens component, in order from theobject side. Embodiment 5 is further characterized by arranging a stop Sfor controlling image brightness and having a radius of curvature r₅between the second lens component and the third lens component of themiddle lens group, by arranging an infrared cutoff filter F with radiiof curvature r₁₀ and r₁₁ between the middle lens group and the rear lensgroup, and by arranging a glass block B on the image-most side of theoptical system.

Embodiment 5 is an optical system having a construction similar to thatof Embodiment 1 but is different from Embodiment 1 in that the thirdlens component is used as the lens component that is moved for focusing.Namely, focusing from the far point to the near point is performed bymoving the third lens component toward the image side. In this manner,Embodiment 5 has an advantage in relaxing the accuracy of positionalcontrol because the extent of the movement for focusing increases. Incomparison with Embodiment 1, Embodiment 5 has more space available inthe vicinity of the lens component that moves for focusing and thusprovides a high degree of freedom in lens frame design.

Embodiment 5 of the present invention satisfies Conditions (1) through(7) above as shown by Table 5 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them. The last lenscomponent in the rear lens group is a cemented lens component, and therefractive indices n(GR_(p)) and n(GR_(n)) and the Abbe numbersv(GR_(p)) and v(GR_(n)) of the lens materials of that lens componentalso satisfy the applicable conditions and design criteria of thepresent invention.

FIGS. 32A-32C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 5 of the present invention whenfocused at the far point on the object side, and FIGS. 32D-32F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 5 of the present invention focused at the near point on theobject side. As shown in FIGS. 32A-32C and FIGS. 32D-32F, in Embodiment5 these aberrations are favorably corrected.

EMBODIMENT 6

FIG. 6 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 6 of the present invention. Table 6 belowlists the various data explained above for Embodiment 6.

TABLE 6 Far point focused state WD = 46 f_(TF) = 1.860 F_(NO) = 4.51 2 ω= 98.6° Near point focused state WD = 23 f_(TN) = 1.796 F_(NO) = 4.38 2ω = 102.4° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.2976 d₂ =0.7000 r₃ = −7.2654 d₃ = 0.5000 n₂ = 1.92286 ν₂ = 18.90 r₄ = −4.0097 d₄= 0.7990 r₅ = ∞(stop) d₅ = 0.5113 r₆ = −6.7995 d₆ = 0.6000 n₃ = 1.80610ν₃ = 40.92 r₇ = −2.5325 d₇ = 0.5223 r₈ = 27.2184 d₈ = 0.3000 n₄ =1.92286 ν₄ = 18.90 r₉ = 3.6263 d₉ = 1.0000 n₅ = 1.58913 ν₅ = 61.14 r₁₀ =−3.9081 d₁₀ = 0.8635 r₁₁ = 6.4748 d₁₁ = 0.7500 n₆ = 1.48749 ν₆ = 70.23r₁₂ = −12.0116 d₁₂ = 0.1000 r₁₃ = ∞ d₁₃ = 0.4500 n₇ = 1.51800 ν₇ = 75.00r₁₄ = ∞ d₁₄ = 0.6000 r₁₅ = ∞ d₁₅ = 3.6000 n₈ = 1.48749 ν₈ = 70.23 r₁₆ =∞ (image plane) |f_(UM)/f_(TF)| = 2.533 f_(U1)/f_(TF) = −0.908f_(TN)/f_(TF) = 0.966 f_(U1) = −1.689 f_(U1)/f_(TF) = −0.91 f_(U2) =9.031 f_(U2)/f_(TF) = 4.86 f_(U3) = 4.711 f_(U3)/f_(TF) = 2.53 f_(U4) =10.227 f_(U4)/f_(TF) = 5.55 f_(UR) = 8.746 f_(UR)/f_(TF) = 4.70 |f_(U)(GM, GR)|_(min) = 2.53 |R (GM, GR)|_(min) = 1.36

As shown in FIG. 6, the optical system of Embodiment 6 is composed of: afront lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₁ and r₂; a middle lens groupthat consists of three lens components, specifically, a second lenselement having positive refractive power and radii of curvature r₃ andr₄, a third lens element having positive refractive power and radii ofcurvature r₆ and r₇, and a fourth lens component that consists of acemented lens component made up of a meniscus lens element havingnegative refractive power cemented to a biconvex lens element with radiiof curvature r₈, r₉, and r₁₀; and a rear lens group that consists of alens component that has positive refractive power and is formed of asingle lens element with lens surfaces having radii of curvature r₁₁ andr₁₂.

Embodiment 6 is an example of an optical system according to the firstand second modes of construction of the present invention describedabove with regard to the middle lens group, referenced by “GM” in Table6 above and in FIG. 6, that is composed of three lens components,namely, a second lens component having positive refractive power, athird lens component, and a cemented fourth lens component havingpositive refractive power, in order from the object side. The third lenscomponent is moved for focusing. A stop S for controlling imagebrightness and having a radius of curvature r₅ is arranged between thesecond lens component and the third lens component of the middle lensgroup, an infrared cutoff filter F with radii of curvature r₁₃ and r₁₄is arranged on the image side of the rear lens group, and a glass blockB with radii of curvature r₁₅ and r_(l6) is arranged on the image sideof the infrared cutoff filter F.

In Embodiment 6, the fourth lens component, which is in the middle lensgroup, is a cemented lens component, and the last lens component on theimage side of the optical system is a single lens element. Aberrationscan be favorably corrected by changing the position of the cemented lenscomponent.

Embodiment 6 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 6 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them.

FIGS. 33A-33C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 6 of the present invention whenfocused at the far point on the object side, and FIGS. 33D-33F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 6 of the present invention when focused at the near point onthe object side. As shown in FIGS. 33A-33C and FIGS. 33D-33F, inEmbodiment 6 these aberrations are favorably corrected.

EMBODIMENT 7

FIG. 7 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 7 of the present invention. Table 7 belowlists the various data explained above for Embodiment 7.

TABLE 7 Far point focused state WD = 46 f_(TF) = 1.812 F_(NO) = 4.55 2ω= 98.6° Near point focused state WD = 23 f_(TN) = 1.831 F_(NO) = 4.62 2ω = 96.9° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.4371 d₂ =0.6000 r₃ = −9.4820 d₃ = 1.1127 n₂ = 1.71999 ν₂ = 50.23 r₄ = −3.0640 d₄= 0.5702 r₅ = ∞ (stop) d₅ = 0.6884 r₆ = −2.9713 d₆ = 0.6500 n₃ = 1.72916ν₃ = 54.68 r₇ = −2.4754 d₇ = 0.5269 r₈ = ∞ d₈ = 0.7000 n₄ = 1.72916 ν₄ =54.68 r₉ = −3.6979 d₉ = 0.4000 r₁₀ = ∞ d₁₀ = 0.4500 n₅ = 1.51800 ν₅ =75.00 r₁₁ = ∞ d₁₁ = 0.1000 r₁₂ = 10.1461 d₁₂ = 1.0000 n₆ = 1.58913 ν₆ =61.14 r₁₃ = −2.4500 d₁₃ = 0.3000 n₇ = 1.92286 ν₇ = 18.90 r₁₄ = −5.9718d₁₄ = 0.6000 r₁₅ = ∞ d₁₅ = 3.6000 n₈ = 1.48749 ν₈ = 70.23 r₁₆ = ∞ (imageplane) |f_(UM)/f_(TF)| = 2.799 f_(U1)/f_(TF) = −1.033 f_(TN)/f_(TF) =1.010 f_(U1) = −1.871 f_(U1)/f_(TF) = −1.03 f_(U2) = 5.862 f_(U2)/f_(TF)= 3.24 f_(U3) = 13.101 f_(U3)/f_(TF) = 7.23 f_(U4) = 5.072 f_(U4)/f_(TF)= 2.80 f_(UR) = 12.907 f_(UR)/f_(TF) = 7.12 |f_(U) (GM, GR)|_(min) =2.80 |R (GM, GR)|_(min) = 1.35 n(GR_(p)) = n₆ = 1.58913 n(GR_(n)) = n₇ =1.92286 ν(GR_(p)) = ν₆ = 61.14 ν(GR_(n)) = ν₇ = 18.90

As shown in FIG. 7, the optical system of Embodiment 7 is composed of: afront lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₁ and r₂; a middle lens groupthat consists of three lens components that are all single lens elementshaving positive refractive power, specifically, a second lens elementhaving radii of curvature r₃ and r₄, a third lens element having radiiof curvature r₆ and r₇, and a fourth lens element having radii ofcurvature r₈ and r₉; and a rear lens group that consists of a cementedlens component made up of a biconvex lens element cemented to a meniscuslens element having negative refractive power with radii of curvaturer₁₂, r₁₃, and r₁₄. Embodiment 7 is an example of an optical systemaccording to the first and second modes of construction of the presentinvention described above with regard to the middle lens group,referenced by “GM” in Table 7 above and in FIG. 7, and is composed ofthree lens components, namely, a second lens component having positiverefractive power, a third lens component, and a fourth lens component,in order from the object side. A stop S for controlling image brightnessis arranged between the second lens component and the third lenscomponent in the middle lens group. An infrared cutoff filter F isarranged between the fourth lens component and the rear or image-sidelens component, and a glass block B, having radii of curvature r₁₅ andr₁₆, is arranged on the image side of the rear lens component.

Embodiment 7 is of a construction similar to Embodiments 1 and 5described above but is different from them in that the fourth lenscomponent is used as the lens component that is moved for focusing, andnear point focusing is performed by moving the fourth lens componenttoward the object side.

Embodiment 7 of the present invention satisfies Conditions (1) through(7) above. The focal lengths f_(U)(GM,GR) of the lens components in themiddle lens group and rear lens group and the radii of curvatureR(GM,GR) of the lens surfaces of the lens components in the middle lensgroup and rear lens group also satisfy the applicable conditions anddesign criteria specified for them. As described above, the last lenscomponent is a cemented lens component, and the refractive indicesn(GR_(p)) and n(GR_(n)) and the Abbe numbers v(GR_(p)) and v(GR_(n)) ofthe lens materials of that lens component also satisfy the applicableconditions and design criteria of the present invention.

FIGS. 34A-34C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 7 of the present invention whenfocused at the far point on the object side, and FIGS. 34D-34F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 7 of the present invention when focused at the near point onthe object. As shown in FIGS. 34A-34C and FIGS. 34D-34F, in Embodiment 7these aberrations are favorably corrected.

EMBODIMENT 8

FIG. 8 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 8 of the present invention. Table 8 belowlists the various data explained above for Embodiment 8.

TABLE 8 Far point focused state WD = 46 f_(TF) = 1.866 F_(NO) = 4.51 2 ω= 98.6° Near point focused state WD = 23 f_(TN) = 1.881 F_(NO) = 4.57 2ω = 97.0° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.5056 d₂ =1.5826 r₃ = 7.9079 (stop) d₃ = 0.5000 n₂ = 1.84666 ν₂ = 23.78 r₄ =−7.9079 d₄ = 0.3363 r₅ = −3.4604 d₅ = 0.3000 n₃ = 1.88300 ν₃ = 40.76 r₆= 2.9554 d₆ = 0.7500 n₄ = 1.72916 ν₄ = 54.68 r₇ = −2.3002 d₇ = 0.5674 r₈= −17.0326 d₈ = 0.6500 n₅ = 1.72916 ν₅ = 54.68 r₉ = −4.0141 d₉ = 0.4000r₁₀ = 13.8240 d₁₀ = 0.9200 n₆ = 1.75500 ν₆ = 52.32 r₁₁ = −3.1803 d₁₁ =0.3000 n₇ = 1.92286 ν₇ = 18.90 r₁₂ = −10.7425 d₁₂ = 0.1000 r₁₃ = ∞ d₁₃ =0.4500 n₈ = 1.51800 ν₈ = 75.00 r₁₄ = ∞ d₁₄ = 0.8000 r₁₅ = ∞ d₁₅ = 3.6000n₉ = 1.48749 ν₉ = 70.23 r₁₆ = ∞ (image plane) |f_(UM)/f_(TF)| = 3.780f_(U1)/f_(TF) = −1.050 f_(TN)/f_(TF) = 1.008 f_(U1) = −1.960f_(U1)/f_(TF) = −1.05 f_(U2) = 4.739 f_(U2)/f_(TF) = 2.54 f_(U3) =15.857 f_(U3)/f_(TF) = 8.50 f_(U4) = 7.054 f_(U4)/f_(TF) = 3.78 f_(UR) =11.528 f_(UR)/f_(TF) = 6.18 |f_(U) (GM, GR)|_(min) = 2.54 |R (GM,GR)|_(min) = 1.23 n(GR_(p)) = n₆ = 1.75500 n(GR_(n)) = n₇ = 1.92286ν(GR_(p)) = ν₆ = 52.32 ν(GR_(n)) = ν₇ = 18.90

As shown in FIG. 8, the optical system of Embodiment 8 is composed of: afront lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₁ and r₂; a middle lens groupthat consists of three lens components, specifically, a second lenscomponent formed as a single lens element having positive refractivepower and radii of curvature r₃ and r₄, a cemented third lens componentcomposed of a biconcave lens element cemented to a biconvex lens elementand having radii of curvature r₅, r₆, and r₇, and a fourth lenscomponent formed as a single lens element having positive refractivepower and radii of curvature r₈ and r₉; and a rear lens group thatconsists of a cemented lens component made up of a biconvex lens elementcemented to a meniscus lens element having negative refractive powerwith radii of curvature r₁₀, r₁₁, and r₁₂ Embodiment 8 is an example ofan optical system according to the first and second modes ofconstruction of the present invention described above with regard to themiddle lens group, referenced by “GM” in Table 8 above and in FIG. 8,being composed of second, third, and fourth lens components havingpositive refractive power. A stop S for controlling image brightness ispositioned on the object side of the second lens component. An infraredcutoff filter F, having radii of curvature r₁₃ and r₁₄, and a glassblock B, having radii of curvature r₁₅ and r₁₆, are arranged on theimage side of the rear lens component.

In Embodiments 1 through 7 described above, the stop S for controllingimage brightness is arranged between the second and third lenscomponents in contrast to Embodiment 8 where the stop S is arranged atthe object-side surface of the second lens component. This has theadvantage that a space can be provided between the first lens componentand the second lens component for placement of a light directing prismto redirect the field of view to the side.

Embodiment 8 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 8 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them. As described above,the refractive indices n(GR_(p)) and n(GR_(n)) and the Abbe numbersv(GR_(p)) and v(GR_(n)) of the lens materials of the cemented lenscomponent that is the last lens component in the rear lens group alsosatisfy the applicable conditions and design criteria of the presentinvention.

FIGS. 35A-35C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 8 of the present invention whenfocused at the far point on the object side, and FIGS. 35D-35F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 8 of the present invention when focused at the near point onthe object side. As shown in FIGS. 35A-35C and FIGS. 35D-35F, inEmbodiment 8 these aberrations are favorably corrected.

EMBODIMENT 9

FIG. 9 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 9 of the present invention. Table 9 belowlists the various data explained above for Embodiment 9.

TABLE 9 Far point focused state WD = 47 f_(TF) = 1.760 F_(NO) = 4.49 2 ω= 103.6° Near point focused state WD = 23 f_(TN) = 1.710 F_(NO) = 4.37 2ω = 106.8° r₁ = ∞ d₁ = 0.7000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ = 0.2900r₃ = 22.2791 d₃ = 0.3000 n₂ = 1.88300 ν₂ = 40.76 r₄ = 1.1037 d₄ = 0.5000r₅ = ∞ d₅ = 0.6965 n₃ = 1.92286 ν₃ = 18.90 r₆ = −4.7015 d₆ = 0.1000 r₇ =∞ (stop) d₇ = 0.3921 r₈ = −4.5000 d₈ = 0.6500 n₄ = 1.48749 ν₄ = 70.23 r₉= −1.6095 d₉ = 0.4834 r₁₀ = −8.1470 d₁₀ = 0.3000 n₅ = 1.88300 ν₅ = 40.76r₁₁ = 3.7013 d₁₁ = 1.3200 n₆ = 1.71999 ν₆ = 50.23 r₁₂ = −3.1017 d₁₂ =0.1000 r₁₃ = 8.5390 d₁₃ = 1.1500 n₇ = 1.71999 ν₇ = 50.23 r₁₄ = −2.7302d₁₄ = 0.3000 n₈ = 1.92286 ν₈ = 18.90 r₁₅ = −6.7728 d₁₅ = 0.4788 r₁₆ = ∞d₁₆ = 0.4500 n₉ = 1.51800 ν₉ = 75.00 r₁₇ = ∞ d₁₇ = 0.3000 r₁₈ = ∞ d₁₈ =3.9000 n₁₀ = 1.51633 ν₁₀ = 64.14 r₁₉ = ∞ (image plane) |f_(UM)/f_(TF)| =2.720 f_(U1)/f_(TF) = −0.752 f_(TN)/f_(TF) = 0.972 f_(U1) = −1.324f_(U1)/f_(TF) = −0.75 f_(U2) = 5.095 f_(U2)/f_(TF) = 2.90 f_(U3) = 4.787f_(U3)/f_(TF) = 2.72 f_(U4) = 9.071 f_(U4)/f_(TF) = 5.15 f_(UR) = 7.019f_(UR)/f_(TF) = 3.99 |f_(U) (GM, GR)|_(min) = 2.72 |R (GM, GR)|_(min) =0.91 n(GR_(p)) = n₇ = 1.71999 n(GR_(n)) = n₈ = 1.92286 ν(GR_(p)) = ν₇ =50.23 ν(GR_(n)) = ν₈ = 18.90

As shown in FIG. 9, the optical system of Embodiment 9 is composed of: afront lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₃ and r₄; a middle lens groupthat consists of three lens components, specifically, a second lenscomponent formed as a single lens element having positive refractivepower and radii of curvature r₅ and r₆, a third lens component formed asa single lens element having positive refractive power and radii ofcurvature r₈ and r₉, and a cemented fourth lens component composed of abiconcave lens element cemented to a biconvex lens element and havingradii of curvature r₁₀, r₁₁, and r₁₂; and a rear lens group thatconsists of a cemented lens component formed of a biconvex lens elementcemented to a meniscus lens element having negative refractive powerwith radii of curvature r₁₃, r₁₄, and r₁₅.

Embodiment 9 is an example of an optical system according to the firstand second modes of construction of the present invention describedabove with regard to the middle lens group, referenced by “GM” in Table9 above and in FIG. 9, being composed of second, third, and fourth lenscomponents having positive refractive power.

Embodiment 9 has a construction in which the fourth lens component,which is in the middle lens group, is a cemented lens component ratherthan a single lens element, as in Embodiment 5 above. A sapphire planeparallel plate C having radii of curvature r₁ and r₂ is arranged on theobject side of the first lens component and that first lens component isformed as a single lens element having negative refractive power and ismade of a glass with a higher refractive index than sapphire. In thismanner, when sapphire having birefringence is used as a lens elementwith optical power as in Embodiments 1 through 8 above, somedeterioration of imaging performance due to polarization dependence ofrefractive power occurs, that is avoided in Embodiment 9. Embodiment 9has an advantage in that the first lens component does not provide thefront surface of the endoscope, thereby providing more freedom inselecting the glass material and bending choices of the first lenscomponent.

In the middle lens group of Embodiment 9, the third lens component isthe lens component that is moved for focusing, and the fourth lenscomponent does not move. Therefore, in Embodiment 9, the fourth lenscomponent does not have to be unreasonably miniaturized and may be madeto have an outside diameter that is nearly the same as the lenscomponent of the rear lens group.

A stop S for controlling image brightness is positioned on the imageside of the second lens component of the middle lens group.

Embodiment 9 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 9 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them.

In Embodiment 9, the image side lens component that forms the rear lensgroup is a cemented lens component, and, as described above, therefractive indices n(GR_(p)) and n(GR_(n)) and the Abbe numbersv(GR_(p)) and v(GR_(n)) of the lens materials of the cemented lenscomponent that is the last lens component satisfy the applicableconditions and design criteria of the present invention.

FIGS. 36A-36C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 9 of the present invention whenfocused at the far point on the object side, and FIGS. 36D-36F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 9 of the present invention when focused at the near point onthe object side. As shown in FIGS. 36A-36C and FIGS. 36D-36F, inEmbodiment 9 these aberrations are favorably corrected.

EMBODIMENT 10

FIG. 10 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 10 of the present invention. Table 10 belowlists the various data explained above for Embodiment 10.

TABLE 10 Far point focused state WD = 47 f_(TF) = 1.760 F_(NO) = 4.47 2ω = 103.8° Near point focused state WD = 23 f_(TN) = 1.711 F_(NO) = 4.362 ω = 106.4° r₁ = ∞ d₁ = 0.7000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ =0.2900 r₃ = 12.8863 d₃ = 0.3000 n₂ = 1.88300 ν₂ = 40.76 r₄ = 1.1823 d₄ =0.5000 r₅ = ∞ d₅ = 0.4827 n₃ = 1.92286 ν₃ = 18.90 r₆ = −5.9310 d₆ =0.1000 r₇ = ∞ (stop) d₇ = 0.4140 r₈ = −6.9710 d₈ = 0.3000 n₄ = 1.88300ν₄ = 40.76 r₉ = 10.5719 d₉ = 1.1000 n₅ = 1.51742 ν₅ = 52.43 r₁₀ =−1.8700 d₁₀ = 0.4940 r₁₁ = −9.6060 d₁₁ = 0.7000 n₆ = 1.83481 ν₆ = 42.71r₁₂ = −3.3249 d₁₂ = 0.1000 r₁₃ = 10.1397 d₁₃ = 1.1500 n₇ = 1.72916 ν₇ =54.68 r₁₄ = −2.7293 d₁₄ = 0.3000 n₈ = 1.92286 ν₈ = 18.90 r₁₅ = −9.6856d₁₅ = 0.4908 r₁₆ = ∞ d₁₆ = 0.4500 n₉ = 1.51800 ν₉ = 75.00 r₁₇ = ∞ d₁₇ =0.3000 r₁₈ = ∞ d₁₈ = 3.9000 n₁₀ = 1.51633 ν₁₀ = 64.14 r₁₉ = ∞ (imageplane) |f_(UM)/f_(TF)| = 3.718 f_(U1)/f_(TF) = −0.848 f_(TN)/f_(TF) =0.972 f_(U1) = −1.492 f_(U1)/f_(TF) = −0.85 f_(U2) = 6.427 f_(U2)/f_(TF)= 3.65 f_(U3) = 6.544 f_(U3)/f_(TF) = 3.72 f_(U4) = 5.797 f_(U4)/f_(TF)= 3.29 f_(UR) = 10.527 f_(UR)/f_(TF) = 5.98 |f_(U) (GM, GR)|_(min) =3.29 |R (GM, GR)|_(min) = 1.06 n(GR_(p)) = n₇ = 1.72916 n GR_(n)) = n₈ =1.92286 ν(GR_(p)) = ν₇ = 54.68 ν(GR_(n)) = ν₈ = 18.90

As shown in FIG. 10, the optical system of Embodiment 10 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₃ and r₄; a middle lens groupthat consists of three lens components, specifically, a second lenscomponent formed as a single lens element having positive refractivepower and radii of curvature r₅ and r₆, a cemented third lens componentcomposed of a biconcave lens element cemented to a biconvex lens elementand having radii of curvature r₈, r₉, and r₁₀, and a fourth lenscomponent formed as a single lens element having positive refractivepower and radii of curvature r₁₁ and r₁₂; and a rear lens group thatconsists of a cemented lens component formed of a biconvex lens elementcemented to a meniscus lens element having negative refractive powerwith radii of curvature r₁₃, r₁₄, and r₁₅.

Embodiment 10 is an example of an optical system according to the secondmode of construction of the present invention described above withregard to the middle lens group, referenced by “GM” in Table 10 aboveand in FIG. 10, being composed of second, third, and fourth lenscomponents having positive refractive power.

Embodiment 10 has a construction that is similar to Embodiment 9 but inEmbodiment 10 the third lens component, which is the lens component thatis moved for focusing, is a cemented lens component rather than a singlelens component and the fourth lens component is a single lens elementrather than a cemented lens component.

Embodiment 10 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 10 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them. In Embodiment 10, theimage side lens component that forms the rear lens group is a cementedlens component, and, as described above, the refractive indicesn(GR_(p)) and n(GR_(n)) and the Abbe numbers v(GR_(p)) and v(GR_(n)) ofthe lens materials of the cemented lens component that is the last lenscomponent satisfy the applicable conditions and design criteria of thepresent invention.

FIGS. 37A-37C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 10 of the present invention whenfocused at the far point on the object side, and FIGS. 37D-37F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 10 of the present invention when focused at the near point onthe object side. As shown in FIGS. 37A-37C and FIGS. 37D-37F, inEmbodiment 10 these aberrations are favorably corrected.

EMBODIMENT 11

FIG. 11 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 11 of the present invention. Table 11 belowlists the various data explained above for Embodiment 11.

TABLE 11 Far point focused state WD = 48 f_(TF) = 1.750 F_(NO) = 4.51 2ω = 103.0° Near point focused state WD = 23 f_(TN) = 1.693 F_(NO) = 4.372 ω = 106.3° r₁ = ∞ d₁ = 0.7000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ =0.2900 r₃ = 11.5644 d₃ = 0.3000 n₂ = 1.88300 ν₂ = 40.76 r₄ = 1.0748 d₄ =0.5300 r₅ = −25.0632 d₅ = 0.5121 n₃ = 1.92286 ν₃ = 18.90 r₆ = −4.2922 d₆= 0.1000 r₇ = ∞ (stop) d₇ = 0.4326 r₈ = −6.2182 d₈ = 0.3000 n₄ = 1.88300ν₄ = 40.76 r₉ = 4.6833 d₉ = 0.9500 n₅ = 1.71999 ν₅ = 50.23 r₁₀ = −1.9693d₁₀ = 0.4823 r₁₁ = −64.8065 d₁₁ = 0.3000 n₆ = 1.88300 ν₆ = 40.76 r₁₂ =4.7301 d₁₂ = 1.1000 n₇ = 1.51633 ν₇ = 64.14 r₁₃ = −3.3095 d₁₃ = 0.1000r₁₄ = 9.1534 d₁₄ = 1.0500 n₈ = 1.72916 ν₈ = 54.68 r₁₅ = −3.1961 d₁₅ =0.3000 n₉ = 1.92286 ν₉ = 18.90 r₁₆ = −7.4233 d₁₆ = 0.4787 r₁₇ = ∞ d₁₇ =0.4500 n₁₀ = 1.51800 ν₁₀ = 75.00 r₁₈ = ∞ d₁₈ = 0.3000 r₁₉ = ∞ d₁₉ =3.9000 n₁₁ = 1.51633 ν₁₁ = 64.14 r₂₀ = ∞ (image plane) |f_(UM)/f_(TF)| =2.462 f_(U1)/f_(TF) = −0.777 f_(TN)/f_(TF) = 0.967 f_(U1) = −1.360f_(U1)/f_(TF) = −0.78 f_(U2) = 5.546 f_(U2)/f_(TF) = 3.17 f_(U3) = 4.308f_(U3)/f_(TF) = 2.46 f_(U4) = 13.267 f_(U4)/f_(TF) = 7.58 f_(UR) = 7.150f_(UR)/f_(TF) = 4.09 |f_(U) (GM, GR)|_(min) = 2.46 |R (GM, GR)|_(min) =1.13 n(GR_(p)) = n₈ = 1.72916 n(GR_(n)) = n₉ = 1.92286 ν(GR_(p)) = ν₈ =54.68 ν(GR_(n)) = ν₉ = 18.90

As shown in FIG. 11, the optical system of Embodiment 11 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₃ and r₄; a middle lens groupthat consists of three lens components, specifically, a second lenscomponent formed as a single lens element having positive refractivepower and radii of curvature r₅ and r₆, a cemented third lens componentcomposed of a biconcave lens element cemented to a biconvex lens elementand having radii of curvature r₈, r₉, and r₁₀, and a cemented fourthlens component composed of a biconcave lens element cemented to abiconvex lens element and having radii of curvature r₁₁, r₁₂, and r₁₃;and a rear lens group composed of a cemented lens component formed of abiconvex lens element cemented to a meniscus lens element havingnegative refractive power with radii of curvature r₁₄, r₁₅, and r₁₆.

Embodiment 11 is an example of an optical system with the middle lensgroup, referenced by “GM” in Table 11 above and in FIG. 11, beingcomposed of second, third, and fourth lens components having positiverefractive power, and is in accordance with the first and second modesof construction of the present invention described above. In Embodiment11, the fourth lens component, which is in the middle lens group, is acemented lens component rather than a single lens element as inEmbodiment 10 above.

In the optical systems of the present invention, the lens component onthe image side of the stop S easily becomes a meniscus lens element witha convex surface on the image side. In that case, if that lens componentis constructed as a single lens element, it becomes difficult toaccurately form the shape of the lens surface. In Embodiment 11, theoptical system can be constructed by lens elements with good workabilityby making the third and fourth lens components, which are in the middlelens group, that easily become meniscus lens elements into cemented lenscomponents.

Similar to Embodiment 2 above, Embodiment 11 is favorable in correctingthe field curvature, which is readily overcorrected.

Embodiment 11 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 11 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them.

In Embodiment 11, the image side lens component that forms the rear lensgroup is a cemented lens component, and, as described above, therefractive indices n(GR_(p)) and n(GR_(n)) and the Abbe numbersv(GR_(p)) and v(GR_(n)) of the lens materials of the cemented lenscomponent that is the last lens component satisfy the applicableconditions and design criteria of the present invention.

FIGS. 38A-38C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 11 of the present invention whenfocused at the far point on the object side, and FIGS. 38D-38F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 11 of the present invention when focused at the near point onthe object side. As shown in FIGS. 38A-38C and FIGS. 38D-38F, inEmbodiment 11 these aberrations are favorably corrected.

EMBODIMENT 12

FIG. 12 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 12 of the present invention. Table 12 belowlists the various data explained above for Embodiment 12.

TABLE 12 Far point focused state WD = 46 f_(TF) = 1.760 F_(NO) = 4.48 2ω = 103.1° Near point focused state WD = 23 f_(TN) = 1.717 F_(NO) = 4.382 ω = 105.3° r₁ = ∞ d₁ = 0.7000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ =0.2900 r₃ = 12.7963 d₃ = 0.3000 n₂ = 1.88300 ν₂ = 40.76 r₄ = 1.1366 d₄ =0.4500 r₅ = 11.9331 d₅ = 0.2500 n₃ = 1.88300 ν₃ = 40.76 r₆ = 2.0645 d₆ =0.5000 n₄ = 1.72825 ν₄ = 28.46 r₇ = −4.4991 d₇ = 0.0500 r₈ = ∞ (stop) d₈= 0.6840 r₉ = −2.7489 d₉ = 0.6200 n₅ = 1.48749 ν₅ = 70.23 r₁₀ = −1.6745d₁₀ = 0.5571 r₁₁ = −8.6245 d₁₁ = 0.7000 n₆ = 1.88300 ν₆ = 40.76 r₁₂ =−3.2679 d₁₂ = 0.1000 r₁₃ = 8.9926 d₁₃ = 1.2000 n₇ = 1.72916 ν₇ = 54.68r₁₄ = −2.4835 d₁₄ = 0.3000 n₈ = 1.92286 ν₈ = 18.90 r₁₅ = −7.7750 d₁₅ =0.4948 r₁₆ = ∞ d₁₆ = 0.4500 n₉ = 1.51800 ν₉ = 75.00 r₁₇ = ∞ d₁₇ = 0.3000r₁₈ = ∞ d₁₈ = 3.9000 n₁₀ = 1.51633 ν₁₀ = 64.14 r₁₉ = ∞ (image plane)|f_(UM)/f_(TF)| = 4.199 f_(U1)/f_(TF) = −0.813 f_(TN)/f_(TF) = 0.976f_(U1) = −1.430 f_(U1)/f_(TF) = −0.81 f_(U2) = 6.272 f_(U2)/f_(TF) =3.56 f_(U3) = 7.391 f_(U3)/f_(TF) = 4.20 f_(U4) = 5.615 f_(U4)/f_(TF) =3.19 f_(UR) = 8.378 f_(UR)/f_(TF) = 4.76 |f_(U) (GM, GR)|_(min) = 3.19|R (GM, GR)|_(min) = 1.16 n(GR_(p)) = n₇ = 1.72916 n(GR_(n)) = n₈ =1.92286 ν(GR_(p)) = ν₇ = 54.68 ν(GR_(n)) = ν₈ = 18.90

As shown in FIG. 12, the optical system of Embodiment 12 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₃ and r₄; a middle lens groupthat consists of three lens components, specifically, a cemented secondlens component formed of a meniscus lens element having negativerefractive power cemented to a biconvex lens element with radii ofcurvature r₅, r₆, and r₇, a third lens component that has positiverefractive power and is formed of a single lens element with lenssurfaces having radii of curvature r₉ and r₁₀, and a fourth lenscomponent that has positive refractive power and is formed of a singlelens element with lens surfaces having radii of curvature r₁₁ and r₁₂;and a rear lens group composed of a cemented lens component formed of abiconvex lens element cemented to a meniscus lens element havingnegative refractive power with radii of curvature r₁₃, r₁₄, and r₁₅.Focusing from the far point to the near point is performed by moving thethird lens component toward the image side. A stop S with radius ofcurvature r₈ for controlling image brightness is arranged between thesecond lens component and the third lens component.

Embodiment 12 is an example of an optical system according to the firstand second modes of construction of the present invention with themiddle lens group, referenced by “GM” in Table 12 above and in FIG. 12,being composed of second, third, and fourth lens components havingpositive refractive power.

Embodiment 12 is very similar to Embodiment 5 except that in Embodiment12 the second lens component is a cemented lens component rather than asingle lens element.

Embodiment 12 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 12 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them.

In Embodiment 12, the image side lens component that forms the rear lensgroup is a cemented lens component, and, as described above, therefractive indices n(GR_(p)) and n(GR_(n)) and the Abbe numbersv(GR_(p)) and v(GR_(n)) of the lens materials of the cemented lenscomponent that is the last lens component satisfy the applicableconditions and design criteria of the present invention.

FIGS. 39A-39C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 12 of the present invention whenfocused at the far point on the object side, and FIGS. 39D-39F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 12 of the present invention when focused at the near point onthe object side. As shown in FIGS. 39A-39C and FIGS. 39D-39F, inEmbodiment 12 these aberrations are favorably corrected.

EMBODIMENT 13

FIG. 13 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 13 of the present invention. Table 13 belowlists the various data explained above for Embodiment 13.

TABLE 13 Far point focused state WD = 48 f_(TF) = 1.790 F_(NO) = 4.51 2ω = 98.6° Near point focused state WD = 23 f_(TN) = 1.755 F_(NO) = 4.512 ω = 101.1° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.4015 d₂ =0.8000 r₃ = −16.2330 d₃ = 0.5800 n₂ = 1.77250 ν₂ = 49.60 r₄ = −2.6697 d₄= 0.5669 r₅ = ∞ (stop) d₅ = 0.0500 r₆ = −7.6446 d₆ = 0.3000 n₃ = 1.72916ν₃ = 54.68 r₇ = −30.9574 d₇ = 0.8248 r₈ = −4.0005 d₈ = 0.5000 n₄ =1.72916 ν₄ = 54.68 r₉ = −2.5301 d₉ = 0.1000 r₁₀ = −7.5805 d₁₀ = 0.6000n₅ = 1.72916 ν₅ = 54.68 r₁₁ = −3.0214 d₁₁ = 0.1000 r₁₂ = ∞ d₁₂ = 0.4500n₆ = 1.51800 ν₆ = 75.00 r₁₃ = ∞ d₁₃ = 0.1000 r₁₄ = 5.5511 d₁₄ = 1.1000n₇ = 1.58913 ν₇ = 61.14 r₁₅ = −2.7000 d₁₅ = 0.3000 n₈ = 1.92286 ν₈ =18.90 r₁₆ = −7.1189 d₁₆ = 0.6000 r₁₇ = ∞ d₁₇ = 3.6000 n₉ = 1.48749 ν₉ =70.23 r₁₈ = ∞ (image plane) |f_(UM)/f_(TF)| = 2.268 f_(U1)/f_(TF) =−1.019 f_(TN)/f_(TF) = 0.980 f_(U1) = −1.824 f_(U1)/f_(TF) = −1.02f_(U2) = 4.060 f_(U2)/f_(TF) = 2.27 f_(U3) = −13.998 f_(U3)/f_(TF) =−7.82 f_(U4) = 8.257 f_(U4)/f_(TF) = 4.61 f_(U5) = 6.527 f_(U5)/f_(TF) =3.65 f_(UR) = 8.938 f_(UR)/f_(TF) = 4.99 |f_(U) (GM, GR)|_(min) = 2.27|R (GM, GR)|_(min) = 1.41 n(GR_(p)) = n₇ = 1.58913 n(GR_(n)) = n₈ =1.92286 ν(GR_(p)) = ν₇ = 61.14 ν(GR_(n)) = ν₈ = 18.90

As shown in FIG. 13, the optical system of Embodiment 13 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₁ and r₂; a middle lens groupthat is composed of four lens components, specifically, a second lenscomponent that has positive refractive power and is formed of a singlelens element with lens surfaces having radii of curvature r₃ and r₄, athird lens component that has negative refractive power and is formed ofa single lens element with lens surfaces having radii of curvature r₆and r₇, a fourth lens component that has positive refractive power andis formed of a single lens element with lens surfaces having radii ofcurvature r₈ and r₉, and a fifth lens component that has positiverefractive power and is formed of a single lens element with lenssurfaces having radii of curvature r₁₀ and r₁₁; and a rear lens groupcomposed of a cemented lens component formed of a biconvex lens elementcemented to a meniscus lens element having negative refractive powerwith radii of curvature r₁₄, r₁₅, and r₁₆. Focusing from the far pointto the near point is performed by moving the second lens componenttoward the image side. A stop S with radius of curvature r₅ forcontrolling image brightness is arranged between the second lenscomponent and the third lens component, which are in the middle lensgroup where the ray height is relatively small.

Embodiment 13 is an example of an optical system according to the firstand second modes of construction of the present invention with themiddle lens group, referenced by “GM” in Table 13 above and in FIG. 13,being composed of second, fourth, and fifth lens components havingpositive refractive power. The correction of astigmatism and lateralcolor is made by using a cemented lens component as the image-side orrear lens component.

Embodiment 13 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 13 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them.

In Embodiment 13, the image side lens component that forms the rear lensgroup is a cemented lens component, and, as described above, therefractive indices n(GR_(p)) and n(GR_(n)) and the Abbe numbersv(GR_(p)) and v(GR_(n)) of the lens materials of the cemented lenscomponent that is the last lens component satisfy the applicableconditions and design criteria of the present invention.

FIGS. 40A-40C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 13 of the present invention whenfocused at the far point on the object side, and FIGS. 40D-40F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 13 of the present invention when focused at the near point onthe object side. As shown in FIGS. 40A-40C and FIGS. 40D-40F, inEmbodiment 13 these aberrations are favorably corrected.

EMBODIMENT 14

FIG. 14 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 14 of the present invention. Table 14 belowlists the various data explained above for Embodiment 14.

TABLE 14 Far point focused state WD = 48 f_(TF) = 1.785 F_(NO) = 4.49 2ω = 98.6° Near point focused state WD = 23 f_(TN) = 1.740 F_(NO) = 4.372 ω = 101.8° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.2556 d₂ =0.6500 r₃ = 237.2682 d₃ = 0.5800 n₂ = 1.78800 ν₂ = 47.37 r₄ = −2.4658 d₄= 0.4852 r₅ = ∞ (stop) d₅ = 0.0500 r₆ = −3.6904 d₆ = 0.3000 n₃ = 1.88300ν₃ = 40.76 r₇ = 683.8898 d₇ = 0.4000 r₈ = −7.7738 d₈ = 0.6000 n₄ =1.72916 ν₄ = 54.68 r₉ = −2.0106 d₉ = 0.3967 r₁₀ = −6.3761 d₁₀ = 0.6486n₅ = 1.72916 ν₅ = 54.68 r₁₁ = −3.3230 d₁₁ = 0.1000 r₁₂ = ∞ d₁₂ = 0.4500n₆ = 1.51800 ν₆ = 75.00 r₁₃ = ∞ d₁₃ = 0.1000 r₁₄ = 11.0958 d₁₄ = 1.1000n₇ = 1.58913 ν₇ = 61.14 r₁₅ = −2.2011 d₁₅ = 0.3000 n₈ = 1.92286 ν₈ =18.90 r₁₆ = −4.1426 d₁₆ = 0.6000 r₁₇ = ∞ d₁₇ = 3.6000 n₉ = 1.48749 ν₉ =70.23 r₁₈ = ∞ (image plane) |f_(UM)/f_(TF)| = 2.328 f_(U1)/f_(TF) =−0.916 f_(TN)/f_(TF) = 0.975 f_(U1) = −1.635 f_(U1)/f_(TF) = −0.92f_(U2) = 3.100 f_(U2)/f_(TF) = 1.74 f_(U3) = −4.156 f_(U3)/f_(TF) =−2.33 f_(U4) = 3.563 f_(U4)/f_(TF) = 2.00 f_(U5) = 8.735 f_(U5)/f_(TF) =4.89 f_(UR) = 8.009 f_(UR)/f_(TF) = 4.49 |f_(U) (GM, GR)|_(min) = 1.74|R (GM, GR)|_(min) = 1.13 n(GR_(p)) = n₇ = 1.58913 n(GR_(n)) = n₈ =1.92286 ν(GR_(p)) = ν₇ = 61.14 ν(GR_(n)) = ν₈ = 18.90

As shown in FIG. 14, the optical system of Embodiment 14 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₁ and r₂; a middle lens groupthat is composed of four lens components, specifically, a second lenscomponent that has positive refractive power and is formed of a singlelens element with lens surfaces having radii of curvature r₃ and r₄, athird lens component that has negative refractive power and is formed ofa single lens element with lens surfaces having radii of curvature r₆and r₇, a fourth lens component that has positive refractive power andis formed of a single lens element with lens surfaces having radii ofcurvature r₈ and r₉, and a fifth lens component that has positiverefractive power and is formed of a single lens element with lenssurfaces having radii of curvature r₁₀ and r₁₁; and a rear lens groupcomposed of a cemented lens component formed of a biconvex lens elementcemented to a meniscus lens element having negative refractive powerwith radii of curvature r₁₄, r₁₅, and r₁₆. Focusing from the far pointto the near point is performed by moving the third lens component towardthe object side. A stop S with radius of curvature r₅ for controllingimage brightness is arranged between the second lens component and thethird lens component.

Embodiment 14 is an example of an optical system according to the firstand third modes of construction of the present invention with the middlelens group, referenced by “GM” in Table 14 above and in FIG. 14, beingcomposed of second and fifth lens components having positive refractivepower separated by third and fourth lens components. Embodiment 14 isvery similar to Embodiment 13 in construction but in Embodiment 14 thethird lens component is moved for focusing instead of the second lenscomponent and that third lens component moves toward the object siderather than toward the image side when focusing from the far point tothe near point.

Embodiment 14 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 14 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them.

In Embodiment 14, the image side lens component that forms the rear lensgroup is a cemented lens component, and, as described above, therefractive indices n(GR_(p)) and n(GR_(n)) and the Abbe numbersv(GR_(p)) and v(GR_(n)) of the lens materials of the cemented lenscomponent that is the last lens component satisfy the applicableconditions and design criteria of the present invention.

FIGS. 41A-41C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 14 of the present invention whenfocused at the far point on the object side, and FIGS. 41D-41F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 14 of the present invention when focused at the near point onthe object side. As shown in FIGS. 41A-41C and FIGS. 41D-41F, inEmbodiment 14 these aberrations are favorably corrected.

EMBODIMENT 15

FIG. 15 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 15 of the present invention. Table 15 belowlists the various data explained above for Embodiment 15.

TABLE 15 Far point focused state WD = 46 f_(TF) = 1.800 F_(NO) = 4.47 2ω = 98.6° Near point focused state WD = 23 f_(TN) = 1.808 F_(NO) = 4.522 ω = 97.5° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.3600 d₂ =0.5500 r₃ = −14.8406 d₃ = 0.6080 n₂ = 1.69895 ν₂ = 30.13 r₄ = −2.8154 d₄= 0.7455 r₅ = ∞ (stop) d₅ = 0.3000 n₃ = 1.80518 ν₃ = 25.42 r₆ = 5.1000d₆ = 0.3702 r₇ = −7.6195 d₇ = 0.6500 n₄ = 1.72916 ν₄ = 54.68 r₈ =−2.0504 d₈ = 0.5297 r₉ = −6.5756 d₉ = 0.7332 n₅ = 1.72916 ν₅ = 54.68 r₁₀= −2.8745 d₁₀ = 0.4000 r₁₁ = ∞ d₁₁ = 0.4500 n₆ = 1.51800 ν₆ = 75.00 r₁₂= ∞ d₁₂ = 0.0300 r₁₃ = 122.5433 d₁₃ = 0.9200 n₇ = 1.75500 ν₇ = 52.32 r₁₄= −2.7121 d₁₄ = 0.3000 n₈ = 1.92286 ν₈ = 18.90 r₁₅ = −6.3829 d₁₅ =0.6756 r₁₆ = ∞ d₁₆ = 3.6000 n₉ = 1.48749 ν₉ = 70.23 r₁₇ = ∞ (imageplane) |f_(UM)/f_(TF)| = 3.591 f_(U1)/f_(TF) = −0.983 f_(TN)/f_(TF) =1.004 f_(U1) = −1.770 f_(U1)/f_(TF) = −0.98 f_(U2) = 4.870 f_(U2)/f_(TF)= 2.71 f_(U3) = −6.334 f_(U3)/f_(TF) = −3.52 f_(U4) = 3.667f_(U4)/f_(TF) = 2.04 f_(U5) = 6.464 f_(U5)/f_(TF) = 3.59 f_(UR) = 11.131f_(UR)/f_(TF) = 6.18 |f_(U) (GM, GR)|_(min) = 2.04 |R (GM, GR)|_(min) =1.14 n(GR_(p)) = n₇ = 1.75500 n(GR_(n)) = n₈ = 1.92286 ν(GR_(p)) = ν₇ =52.32 ν(GR_(n)) = ν₈ = 18.90

As shown in FIG. 15, the optical system of Embodiment 15 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₁ and r₂; a middle lens groupthat is composed of four lens components, specifically, a second lenscomponent that has positive refractive power and is formed of a singlelens element with lens surfaces having radii of curvature r₃ and r₄, athird lens component that has negative refractive power and is formed ofa single lens element with lens surfaces having radii of curvature r₅and r₆, a fourth lens component that has positive refractive power andis formed of a single lens element with lens surfaces having radii ofcurvature r₇ and r₈, and a fifth lens component that has positiverefractive power and is formed of a single lens element with lenssurfaces having radii of curvature r₉ and r₁₀; and a rear lens groupcomposed of a cemented lens component formed of a biconvex lens elementcemented to a meniscus lens element having negative refractive powerwith radii of curvature r₁₃, r₁₄, and r₁₅. Focusing from the far pointto the near point is performed by moving the fifth lens component towardthe object side. A stop S for controlling image brightness is arrangedon the object-side surface of the third lens component that has a radiusof curvature r₅.

Embodiment 15 is an example of an optical system according to the firstand third modes of construction of the present invention with the middlelens group, referenced by “GM” in Table 15 above and in FIG. 15, beingcomposed of second and fifth lens components having positive refractivepower separated by third and fourth lens components.

Embodiment 15 is very similar to Embodiments 13 and 14 in constructionbut in Embodiment 15 the fifth lens component is moved for focusinginstead of the second or third lens component. That fifth lens componentmoves toward the object side during focusing from the far point to thenear point.

Embodiment 15 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 15 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them.

In Embodiment 15, the image side lens component that forms the rear lensgroup is a cemented lens component, and, as described above, therefractive indices n(GR_(p)) and n(GR_(n)) and the Abbe numbersv(GR_(p)) and v(GR_(n)) of the lens materials of the cemented lenscomponent that is the last lens component satisfy the applicableconditions and design criteria of the present invention.

FIGS. 42A-42C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 15 of the present invention whenfocused at the far point on the object side, and FIGS. 42D-42F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 15 of the present invention when focused at the near point onthe object side. As shown in FIGS. 42A-42C and FIGS. 42D-42F, inEmbodiment 15 these aberrations are favorably corrected.

EMBODIMENT 16

FIG. 16 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 16 of the present invention. Table 16 belowlists the various data explained above for Embodiment 16.

TABLE 16 Far point focused state WD = 46 f_(TF) = 1.760 F_(NO) = 4.52 2ω = 101.6° Near point focused state WD = 23 f_(TN) = 1.717 F_(NO) = 4.422 ω = 104.2° r₁ = ∞ d₁ = 0.7000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ =0.2900 r₃ = 21.8706 d₃ = 0.3000 n₂ = 1.88300 ν₂ = 40.76 r₄ = 1.2542 d₄ =0.5300 r₅ = 162.1167 d₅ = 0.6417 n₃ = 1.78472 ν₃ = 25.68 r₆ = −3.5000 d₆= 0.1000 r₇ = ∞ (stop) d₇ = 0.0300 r₈ = ∞ d₈ = 0.8361 n₄ = 1.88300 ν₄ =40.76 r₉ = 10.6992 d₉ = 0.4814 r₁₀ = −4.5000 d₁₀ = 0.6000 n₅ = 1.48749ν₅ = 70.23 r₁₁ = −2.0113 d₁₁ = 0.4743 r₁₂ = −10.3986 d₁₂ = 0.7000 n₆ =1.88300 ν₆ = 40.76 r₁₃ = −3.6699 d₁₃ = 0.1000 r₁₄ = 7.6980 d₁₄ = 0.3000n₇ = 1.92286 ν₇ = 18.90 r₁₅ = 2.6490 d₁₅ = 1.2000 n₈ = 1.72916 ν₈ =54.68 r₁₆ = −7.9927 d₁₆ = 0.4489 r₁₇ = ∞ d₁₇ = 0.4500 n₉ = 1.51800 ν₉ =75.00 r₁₈ = ∞ d₁₈ = 0.3000 r₁₉ = ∞ d₁₉ = 3.9000 n₁₀ = 1.51633 ν₁₀ =64.14 r₂₀ = ∞ (image plane) |f_(UM)/f_(TF)|= 3.928 f_(U1)/f_(TF) =−0.862 f_(TN)/f_(TF) = 0.976 f_(U1) = −1.517 f_(U1)/f_(TF) = −0.86f_(U2) = 4.373 f_(U2)/f_(TF) = 2.49 f_(U3) = −12.117 f_(U3)/f_(TF) =−6.89 f_(U4) = 6.914 f_(U4)/f_(TF) = 3.93 f_(U5) = 6.124 f_(U5)/f_(TF) =3.48 f_(UR) = 7.429 f_(UR)/f_(TF) = 4.22 |f_(U) (GM, GR)|_(min) = 2.48|R (GM, GR)|_(min) = 1.14 n(GR_(p)) = n₈ = 1.72916 n(GR_(n)) = n₇ =1.92286 ν(GR_(p)) = ν₈ = 54.68 ν(GR_(n)) = ν₇ = 18.90

As shown in FIG. 16, the optical system of Embodiment 16 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₃ and r₄; a middle lens groupthat is composed of four lens components, specifically, a second lenscomponent that has positive refractive power and is formed of a singlelens element with lens surfaces having radii of curvature r₅ and r₆, athird lens component that has negative refractive power and is formed ofa single lens element with lens surfaces having radii of curvature r₈and r₉, a fourth lens component that has positive refractive power andis formed of a single lens element with lens surfaces having radii ofcurvature r₁₀ and r₁₁, and a fifth lens component that has positiverefractive power and is formed of a single lens element with lenssurfaces having radii of curvature r₁₂ and r₁₃; and a rear lens groupcomposed of a cemented lens with radii of curvature r₁₄, r₁₅, and r₁₆.Focusing from the far point to the near point is performed by moving thefourth lens component toward the image side, and a stop S forcontrolling image brightness is arranged between the second lenscomponent and the third lens component and has a radius of curvature r₇.

Embodiment 16 is an example of an optical system according to the firstand third modes of construction of the present invention with the middlelens group, referenced by “GM” in Table 16 above and in FIG. 16, beingcomposed of second and fifth lens components having positive refractivepower separated by third and fourth lens components.

Embodiment 16 is very similar to Embodiments 13, 14, and 15 inconstruction but in Embodiment 16 the fourth lens component is moved forfocusing, a sapphire plane parallel plate C is arranged on the objectside of the first lens component, and the first lens component is madeof glass with a higher refractive index than sapphire.

Embodiment 16 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 16 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them.

In Embodiment 16, the image side lens component that forms the rear lensgroup is a cemented lens component composed of a lens element havingnegative refractive power and a lens element having positive refractivepower, and, as described above, the refractive indices n(GR_(p)) andn(GR_(n)) and the Abbe numbers v(GR_(p)) and v(GR_(n)) of the lensmaterials of the cemented lens component that is the last lens componentsatisfy the applicable conditions and design criteria of the presentinvention.

FIGS. 43A-43C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 16 of the present invention whenfocused at the far point on the object side, and FIGS. 43D-43F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 16 of the present invention when focused at the near point onthe object side. As shown in FIGS. 43A-43C and FIGS. 43D-43F, inEmbodiment 16 these aberrations are favorably corrected.

EMBODIMENT 17

FIG. 17 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 17 of the present invention. Table 17 belowlists the various data explained above for Embodiment 17.

TABLE 17 Far point focused state WD = 48 f_(TF) = 1.760 F_(NO) = 4.46 2ω = 104.6° Near point focused state WD = 23 f_(TN) = 1.725 F_(NO) = 4.392 ω = 105.9° r₁ = ∞ d₁ = 0.7000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ =0.2900 r₃ = 11.9476 d₃ = 0.3000 n₂ = 1.88300 ν₂ = 40.76 r₄ = 1.1909 d₄ =0.5300 r₅ = 25.1818 d₅ = 0.5702 n₃ = 1.92286 ν₃ = 18.90 r₆ = −22.1060 d₆= 0.0300 r₇ = ∞ (stop) d₇ = 0.4323 r₈ = −5.0000 d₈ = 0.5500 n₄ = 1.51742ν₄ = 52.43 r₉ = −2.5842 d₉ = 0.4849 r₁₀ = −4.3178 d₁₀ = 0.7000 n₅ =1.51633 ν₅ = 64.14 r₁₁ = −2.0618 d₁₁ = 0.1000 r₁₂ = −12.1564 d₁₂ =0.6500 n₆ = 1.72916 ν₆ = 54.68 r₁₃ = −3.8146 d₁₃ = 0.1000 r₁₄ = 8.6985d₁₄ = 1.2000 n₇ = 1.58913 ν₇ = 61.14 r₁₅ = −2.6089 d₁₅ = 0.3000 n₈ =1.92286 ν₈ = 18.90 r₁₆ = −6.1725 d₁₆ = 0.4559 r₁₇ = ∞ d₁₇ = 0.4500 n₉ =1.51800 ν₉ = 75.00 r₁₈ = ∞ d₁₈ = 0.3000 r₁₉ = ∞ d₁₉ = 3.9000 n₁₀ =1.51633 ν₁₀ = 64.14 r₂₀ = ∞ (image plane) |f_(UM)/f_(TF)| = 5.450f_(U1)/f_(TF) = −0.863 f_(TN)/f_(TF) = 0.980 f_(U1) = −1.518f_(U1)/f_(TF) = −0.86 f_(U2) = 12.830 f_(U2)/f_(TF) = 7.29 f_(U3) =9.592 f_(U3)/f_(TF) = 5.45 f_(U4) = 6.912 f_(U4)/f_(TF) = 3.93 f_(U5) =7.381 f_(U5)/f_(TF) = 4.19 f_(UR) = 11.177 f_(UR)/f_(TF) = 6.35 |f_(U)(GM, GR)|_(min) = 3.93 |R (GM, GR)|_(min) = 1.17 n(GR_(p)) = n₇ =1.58913 n(GR_(n)) = n₈ = 1.92286 ν(GR_(p)) = ν₇ = 61.14 ν(GR_(n)) = ν₈ =18.90

As shown in FIG. 17, the optical system of Embodiment 17 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₃ and r₄; a middle lens groupthat is composed of four lens components, specifically, second, third,fourth, and fifth lens components, each of which has positive refractivepower and is formed of a single lens element with lens surfaces havingradii of curvature r₅ and r₆, r₈ and r₉, r₁₀ and r₁₁, and r₁₂ and r₁₃,respectively; and a rear lens group composed of a cemented lenscomponent formed of a biconvex lens element cemented to a meniscus lenselement having negative refractive power with radii of curvature r₁₄,r₁₅, and r₁₆. Focusing from the far point to the near point is performedby moving the third lens component toward the image side, and a stop Sfor controlling image brightness is arranged between the second lenscomponent and the third lens component and has a radius of curvature r₇.A sapphire plane parallel plate C is arranged on the object side of thefirst lens component.

Embodiment 17 is an example of an optical system according to the firstand third modes of construction of the present invention with the middlelens group, referenced by “GM” in Table 17 above and in FIG. 17, beingcomposed of second, third, fourth, and fifth lens components havingpositive refractive power.

Embodiment 17 is very similar to Embodiment 14 in construction but inEmbodiment 17 the third lens component has positive refractive power.

Embodiment 17 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 17 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them. In Embodiment 17, theimage side lens component that forms the rear lens group is a cementedlens component composed of a lens element having positive refractivepower and a lens element having negative refractive power, and, asdescribed above, the refractive indices n(GR_(p)) and n(GR_(n)) and theAbbe numbers v(GR_(p)) and v(GR_(n)) of the lens materials of thecemented lens component that is the last lens component satisfy theapplicable conditions and design criteria of the present invention.

FIGS. 44A-44C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 17 of the present invention whenfocused at the far point on the object side, and FIGS. 44D-44F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 17 of the present invention when focused at the near point onthe object side. As shown in FIGS. 44A-44C and FIGS. 44D-44F, inEmbodiment 17 these aberrations are favorably corrected.

EMBODIMENT 18

FIG. 18 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 18 of the present invention. Table 18 belowlists the various data explained above for Embodiment 18.

TABLE 18 Far point focused state WD = 47 f_(TF) = 1.750 F_(NO) = 4.50 2ω = 102.5° Near point focused state WD = 23 f_(TN) = 1.706 F_(NO) = 4.402 ω = 105.3° r₁ = ∞ d₁ = 0.7000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ =0.2900 r₃ = 12.3202 d₃ = 0.3000 n₂ = 1.88300 ν₂ = 40.76 r₄ = 1.1072 d₄ =0.5000 r₅ = ∞ d₅ = 0.6416 n₃ = 1.92286 ν₃ = 18.90 r₆ = −5.2798 d₆ =0.1000 r₇ = ∞ (stop) d₇ = 0.3788 r₈ = −5.4871 d₈ = 0.6000 n₄ = 1.48749ν₄ = 70.23 r₉ = −1.8874 d₉ = 0.4787 r₁₀ = −5.0755 d₁₀ = 0.3000 n₅ =1.88300 ν₅ = 40.76 r₁₁ = 5.2493 d₁₁ = 1.1700 n₆ = 1.71999 ν₆ = 50.23 r₁₂= −2.9289 d₁₂ = 0.1000 r₁₃ = ∞ d₁₃ = 0.6000 n₇ = 1.72916 ν₇ = 54.68 r₁₄= −6.1168 d₁₄ = 0.1000 r₁₅ = 14.0575 d₁₅ = 0.9500 n₈ = 1.71999 ν₈ =50.23 r₁₆ = −3.1558 d₁₆ = 0.3000 n₉ = 1.92286 ν₉ = 18.90 r₁₇ = −10.2587d₁₇ = 0.4710 r₁₈ = ∞ d₁₈ = 0.4500 n₁₀ = 1.51800 ν₁₀ = 75.00 r₁₉ = ∞ d₁₉= 0.3000 r₂₀ = ∞ d₂₀ = 3.9000 n₁₁ = 1.51633 ν₁₁ = 64.14 r₂₁ = ∞ (imageplane) |f_(UM)/f_(TF)| = 3.198 f_(U1)/f_(TF) = −0.797 f_(TN)/f_(TF) =0.975 f_(U1) = −1.395 f_(U1)/f_(TF) = −0.80 f_(U2) = 5.721 f_(U2)/f_(TF)= 3.27 f_(U3) = 5.596 f_(U3)/f_(TF) = 3.20 f_(U4) = 12.318 f_(U4)/f_(TF)= 7.04 f_(U5) = 8.389 f_(U5)/f_(TF) = 4.79 f_(UR) = 13.102 f_(UR)/f_(TF)= 7.49 |f_(U) (GM, GR)|_(min) = 3.20 |R (GM, GR)|_(min) = 1.08 n(GR_(p))= n₈ = 1.71999 n(GR_(n)) = n₉ = 1.92286 ν(GR_(p)) = ν₈ = 50.23 ν(GR_(n))= ν₉ = 18.90

As shown in FIG. 18, the optical system of Embodiment 18 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₃ and r₄; a middle lens groupthat is composed of four lens components, specifically, a second lenscomponent that has positive refractive power and is formed of a singlelens element with lens surfaces having radii of curvature r₅ and r₆, athird lens component that has positive refractive power and is formed ofa single lens element with lens surfaces having radii of curvature r₈and r₉, a cemented fourth lens component that has positive refractivepower and is formed of a biconcave lens element cemented to a biconvexlens element and having radii of curvature r₁₀, r₁₁, and r₁₂, and afifth lens component that has positive refractive power and is formed ofa single lens element with lens surfaces having radii of curvature r₁₃and r₁₄; and a rear lens group composed of a cemented lens componentformed of a biconvex lens element cemented to a meniscus lens elementhaving negative refractive power with radii of curvature r₁₅, r₁₆, andr₁₇. Focusing from the far point to the near point is performed bymoving the third lens component toward the image side, and a stop S forcontrolling image brightness is arranged between the second lenscomponent and the third lens component.

Embodiment 18 is an example of an optical system according to the firstand third modes of construction of the present invention with the middlelens group, referenced by “GM” in Table 18 above and in FIG. 18, beingcomposed of second, third, fourth, and fifth lens components havingpositive refractive power.

Embodiment 18 is very similar to Embodiment 17 in construction but inEmbodiment 18 the fourth lens component is a cemented lens component.

Embodiment 18 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 18 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them. In Embodiment 18, theimage side lens component that forms the rear lens group is a cementedlens component composed of a lens element having positive refractivepower cemented to a lens element having negative refractive power, and,as described above, the refractive indices n(GR_(p)) and n(GR_(n)) andthe Abbe numbers v(GR_(p)) and v(GR_(n)) of the lens materials of thecemented lens component that is the last lens component satisfy theapplicable conditions and design criteria of the present invention.

FIGS. 45A-45C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 18 of the present invention whenfocused at the far point on the object side, and FIGS. 45D-45F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 18 of the present invention when focused at the near point onthe object side. As shown in FIGS. 45A-45C and FIGS. 45D-45F, inEmbodiment 18 these aberrations are favorably corrected.

EMBODIMENT 19

FIG. 19 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 19 of the present invention. Table 19 belowlists the various data explained above for Embodiment 19.

TABLE 19 Far point focused state WD = 48 f_(TF) = 1.770 F_(NO) = 4.48 2ω = 103.2° Near point focused state WD = 23 f_(TN) = 1.725 F_(NO) = 4.382 ω = 105.7° r₁ = ∞ d₁ = 0.7000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ =0.2900 r₃ = 11.6817 d₃ = 0.3000 n₂ = 1.88300 ν₂ = 40.76 r₄ = 1.2075 d₄ =0.5300 r₅ = 13.1653 d₅ = 0.5550 n₃ = 1.92286 ν₃ = 18.90 r₆ = ∞ d₆ =0.0300 r₇ = ∞ (stop) d₇ = 0.4994 n₄ = 1.84666 ν₄ = 23.78 r₈ = −14.8388d₈ = 0.4380 r₉ = −2.8722 d₉ = 0.6000 n₅ = 1.51742 ν₅ = 52.43 r₁₀ =−1.7104 d₁₀ = 0.4834 r₁₁ = −7.9606 d₁₁ = 0.7000 n₆ = 1.77250 ν₆ = 49.60r₁₂ = −3.0691 d₁₂ = 0.1000 r₁₃ = 11.5500 d₁₃ = 1.3300 n₇ = 1.72916 ν₇ =54.68 r₁₄ = −2.3253 d₁₄ = 0.3000 n₈ = 1.92286 ν₈ = 18.90 r₁₅ = −5.4291d₁₅ = 0.4639 r₁₆ = ∞ d₁₆ = 0.4500 n₉ = 1.51800 ν₉ = 75.00 r₁₇ = ∞ d₁₇ =0.3000 r₁₈ = ∞ d₁₈ = 3.9000 n₁₀ = 1.51633 ν₁₀ = 64.14 r₁₉ = ∞ (imageplane) |f_(UM)/f_(TF)| = 3.926 f_(U1)/f_(TF) = −0.873 f_(TN)/f_(TF) =0.975 f_(U1) = −1.546 f_(U1)/f_(TF) = −0.87 f_(U2) = 14.266f_(U2)/f_(TF) = 8.06 f_(U3) = 17.526 f_(U3)/f_(TF) = 9.90 f_(U4) = 6.949f_(U4)/f_(TF) = 3.93 f_(U5) = 6.086 f_(U5)/f_(TF) = 3.44 f_(UR) = 6.848f_(UR)/f_(TF) = 3.87 |f_(U) (GM, GR)|_(min) = 3.44 |R (GM, GR)|_(min) =0.97 n(GR_(p)) = n₇ = 1.72916 n(GR_(n)) = n₈ = 1.92286 ν(GR_(p)) = ν₇ =54.68 ν(GR_(n)) = ν₈ = 18.90

As shown in FIG. 19, the optical system of Embodiment 19 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₃ and r₄; a middle lens groupthat is composed of four lens components, specifically, second, third,fourth, and fifth lens components, each of which has positive refractivepower and is formed of a single lens element with lens surfaces havingradii of curvature r₅ and r₆, r₇ and r₈, r₉ and r₁₀, and r₁₁ and r₁₂,respectively; and a rear lens group composed of a cemented lenscomponent formed of a biconvex lens element cemented to a meniscus lenselement having negative refractive power with radii of curvature r₁₃,r₁₄, and r₁₅. Focusing from the far point to the near point is performedby moving the fourth lens component toward the image side, and a stop Sfor controlling image brightness is arranged on the object-side surfaceof the third lens component and has a radius of curvature r₇. A sapphireplane parallel plate C is arranged on the object side of the first lenscomponent.

Embodiment 19 is an example of an optical system according to the firstand third modes of construction of the present invention with the middlelens group, referenced by “GM” in Table 19 above and in FIG. 19, beingcomposed of second, third, fourth, and fifth lens components havingpositive refractive power.

Embodiment 19 is very similar to Embodiment 17 in construction but inEmbodiment 19 the fourth lens component moves for focusing.

Embodiment 19 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 19 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them. In Embodiment 19, theimage side lens component that forms the rear lens group is a cementedlens component composed of a lens element having positive refractivepower and a lens element having negative refractive power, and, asdescribed above, the refractive indices n(GR_(p)) and n(GR_(n)) and theAbbe numbers v(GR_(p)) and v(GR_(n)) of the lens materials of thecemented lens component that is the last lens component satisfy theapplicable conditions and design criteria of the present invention.

FIGS. 46A-46C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 19 of the present invention whenfocused at the far point on the object side, and FIGS. 46D-46F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 19 of the present invention when focused at the near point onthe object side. As shown in FIGS. 46A-46C and FIGS. 46D-46F, inEmbodiment 19 these aberrations are favorably corrected.

EMBODIMENT 20

FIG. 20 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 20 of the present invention. Table 20 belowlists the various data explained above for Embodiment 20.

TABLE 20 Far point focused state WD = 45 f_(TF) = 1.740 F_(NO) = 4.52 2ω = 104.1° Near point focused state WD = 23 f_(TN) = 1.700 F_(NO) = 4.422 ω = 106.2° r₁ = ∞ d₁ = 0.7000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ =0.2900 r₃ = 9.2269 d₃ = 0.3000 n₂ = 1.88300 ν₂ = 40.76 r₄ = 1.0952 d₄ =0.5000 r₅ = ∞ d₅ = 0.4535 n₃ = 1.92286 ν₃ = 18.90 r₆ = −5.6726 d₆ =0.1000 r₇ = ∞ (stop) d₇ = 0.3867 r₈ = −4.2341 d₈ = 0.3000 n₄ = 1.88300ν₄ = 40.76 r₉ = ∞ d₉ = 0.8000 n₅ = 1.51742 ν₅ = 52.43 r₁₀ = −1.8200 d₁₀= 0.4852 r₁₁ = −6.9666 d₁₁ = 0.7000 n₆ = 1.51742 ν₆ = 52.43 r₁₂ =−2.7028 d₁₂ = 0.1000 r₁₃ = ∞ d₁₃ = 0.6000 n₇ = 1.71999 ν₇ = 50.23 r₁₄ =−6.3085 d₁₄ = 0.1000 r₁₅ = 26.7285 d₁₅ = 1.0700 n₈ = 1.72916 ν₈ = 54.68r₁₆ = −2.7215 d₁₆ = 0.3000 n₉ = 1.92286 ν₉ = 18.90 r₁₇ = −7.9625 d₁₇ =0.4748 r₁₈ = ∞ d₁₈ = 0.4500 n₁₀ = 1.51800 ν₁₀ = 75.00 r₁₉ = ∞ d₁₉ =0.3000 r₂₀ = ∞ d₂₀ = 3.9000 n₁₁ = 1.51633 ν₁₁ = 64.14 r₂₁ = ∞ (imageplane) |f_(UM)/f_(TF)| = 4.935 f_(U1)/f_(TF) = −0.83 f_(TN)/f_(TF) =0.977 f_(U1) = −1.432 f_(U1)/f_(TF) = −0.82 f_(U2) = 6.147 f_(U2)/f_(TF)= 3.53 f_(U3) = 8.587 f_(U3)/f_(TF) = 4.94 f_(U4) = 8.082 f_(U4)/f_(TF)= 4.65 f_(U5) = 8.762 f_(U5)/f_(TF) = 5.04 f_(UR) = 13.884 f_(UR)/f_(TF)= 7.98 |f_(U) (GM, GR)|_(min) = 3.69 |R (GM, GR)|_(min) = 1.05 n(GR_(p))= n₈ = 1.72916 n(GR_(n)) = n₉ = 1.92286 ν(GR_(p)) = ν₈ = 54.68 ν(GR_(n))= ν₉ = 18.90

As shown in FIG. 20, the optical system of Embodiment 20 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₃ and r₄; a middle lens groupthat is composed of four lens components, specifically, a second lenscomponent that has positive refractive power and is formed of a singlelens element with lens surfaces having radii of curvature r₅ and r₆, acemented third lens component that is formed of a lens element havingnegative refractive power cemented to a lens element having positiverefractive power and having radii of curvature r₈, r₉ and r₁₀, a fourthlens component that has positive refractive power and is formed of asingle lens element and having radii of curvature r₁₁ and r₁₂, and afifth lens component that has positive refractive power and is formed ofa single lens element with lens surfaces having radii of curvature r₁₃and r₁₄; and a rear lens group composed of a cemented lens componentformed of a biconvex lens element cemented to a meniscus lens elementhaving negative refractive power with radii of curvature r₁₅, r₁₆, andr₁₇. Focusing from the far point to the near point is performed bymoving the third lens component toward the image side, and a stop S forcontrolling image brightness is arranged between the second lenscomponent and the third lens component and has a radius of curvature r₇.

Embodiment 20 is an example of an optical system according to the firstand third modes of construction of the present invention with the middlelens group, referenced by “GM” in Table 20 above and in FIG. 20, beingcomposed of the second lens component having positive refractive power,third and fourth lens components, and the fifth lens component havingpositive refractive power.

Embodiment 20 is very similar to Embodiment 17 in construction but inEmbodiment 20 the third lens component is a cemented lens component.

Embodiment 20 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 20 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them. In Embodiment 20, theimage side lens component that forms the rear lens group is a cementedlens component composed of a lens element having positive refractivepower cemented to a lens element having negative refractive power, and,as described above, the refractive indices n(GR_(p)) and n(GR_(n)) andthe Abbe numbers v(GR_(p)) and v(GR_(n)) of the lens materials of thecemented lens component that is the last lens component satisfy theapplicable conditions and design criteria of the present invention.

FIGS. 47A-47C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 20 of the present invention whenfocused at the far point on the object side, and FIGS. 47D-47F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 20 of the present invention when focused at the near point onthe object side. As shown in FIGS. 47A-47C and FIGS. 47D-47F, inEmbodiment 20 these aberrations are favorably corrected.

EMBODIMENT 21

FIG. 21 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 21 of the present invention. Table 21 belowlists the various data explained above for Embodiment 21.

TABLE 21 Far point focused state WD = 48 f_(TF) = 1.760 F_(NO) = 4.51 2ω = 104.0° Near point focused state WD = 23 f_(TN) = 1.714 F_(NO) = 4.412 ω = 106.7° r₁ = ∞ d₁ = 0.7000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ =0.2900 r₃ = 14.9688 d₃ = 0.3000 n₂ = 1.88300 ν₂ = 40.76 r₄ = 1.1155 d₄ =0.5000 r₅ = 8.0101 d₅ = 0.5062 n₃ = 1.84666 ν₃ = 23.78 r₆ = −5.6893 d₆ =0.1000 r₇ = ∞ (stop) d₇ = 0.0800 r₈ = −7.7719 d₈ = 0.3000 n₄ = 1.88300ν₄ = 40.76 r₉ = 4.4560 d₉ = 0.6000 n₅ = 1.51742 ν₅ = 52.43 r₁₀ = −4.3915d₁₀ = 0.4318 r₁₁ = −4.5639 d₁₁ = 0.6800 n₆ = 1.51742 ν₆ = 52.43 r₁₂ =−2.0715 d₁₂ = 0.4871 r₁₃ = −21.0210 d₁₃ = 0.7000 n₇ = 1.88300 ν₇ = 40.76r₁₄ = −4.2364 d₁₄ = 0.1000 r₁₅ = 7.6233 d₁₅ = 1.1500 n₈ = 1.72916 ν₈ =54.68 r₁₆ = −3.0536 d₁₆ = 0.3000 n₉ = 1.92286 ν₉ = 18.90 r₁₇ = −16.0160d₁₇ = 0.4868 r₁₈ = ∞ d₁₈ = 0.4500 n₁₀ = 1.51800 ν₁₀ = 75.00 r₁₉ = ∞ d₁₉= 0.3000 r₂₀ = ∞ d₂₀ = 3.9000 n₁₁ = 1.51633 ν₁₁ = 64.14 r₂₁ = ∞ (imageplane) |f_(UM)/f_(TF)| = 3.811 f_(U1)/f_(TF) = −0.784 f_(TN)/f_(TF) =0.974 f_(U1) = −1.379 f_(U1)/f_(TF) = −0.78 f_(U2) = 3.997 f_(U2)/f_(TF)= 2.27 f_(U3) = −14.706 f_(U3)/f_(TF) = −8.36 f_(U4) = 6.707f_(U4)/f_(TF) = 3.81 f_(U5) = 5.894 f_(U5)/f_(TF) = 3.35 f_(UR) = 11.126f_(UR)/f_(TF) = 6.32 |f_(U) (GM, GR)|_(min) = 2.27 |R (GM, GR)|_(min) =1.18 n(GR_(p)) = n₈ = 1.72916 n(GR_(n)) = n₉ = 1.92286 ν(GR_(p)) = ν₈ =54.68 ν(GR_(n)) = ν₉ = 18.90

As shown in FIG. 21, the optical system of Embodiment 21 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₃ and r₄; a middle lens groupthat is composed of four lens components, specifically, a second lenscomponent that has positive refractive power and is formed of a singlelens element with lens surfaces having radii of curvature r₅ and r₆, acemented third lens component that is formed of a biconcave lens elementcemented to a biconvex lens element and having radii of curvature r₈, r₉and r₁₀, a fourth lens component of meniscus shape that has positiverefractive power and is formed of a single lens element having radii ofcurvature r₁₁ and r₁₂, and a fifth lens component of meniscus shape thathas positive refractive power and is formed of a single lens elementwith lens surfaces having radii of curvature r₁₃ and r₁₄; and a rearlens group composed of a cemented lens component formed of a biconvexlens element cemented to a meniscus lens element having negativerefractive power with radii of curvature r₁₅, r₁₆, and r₁₇. Focusingfrom the far point to the near point is performed by moving the fourthlens component toward the image side, and a stop S for controlling imagebrightness is arranged between the second lens component and the thirdlens component and has a radius of curvature r₇.

Embodiment 21 is an example of an optical system according to the firstand third modes of construction of the present invention with the middlelens group, referenced by “GM” in Table 21 above and in FIG. 21, beingcomposed of the second lens component having positive refractive power,third and fourth lens components, and the fifth lens component havingpositive refractive power.

Embodiment 21 is very similar to Embodiment 16 in construction but inEmbodiment 21 the third lens component is a cemented lens component.

Embodiment 21 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 21 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them. In Embodiment 21, theimage side lens component that forms the rear lens group is a cementedlens component composed of a lens element having positive refractivepower cemented to a lens element having negative refractive power, and,as described above, the refractive indices n(GR_(p)) and n(GR_(n)) andthe Abbe numbers v(GR_(p)) and v(GR_(n)) of the lens materials of thecemented lens component that is the last lens component satisfy theapplicable conditions and design criteria of the present invention.

FIGS. 48A-48C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 21 of the present invention whenfocused at the far point on the object side, and FIGS. 48D-48F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 21 of the present invention when focused at the near point onthe object side. As shown in FIGS. 48A-48C and FIGS. 48D-48F, inEmbodiment 21 these aberrations are favorably corrected.

EMBODIMENT 22

FIG. 22 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 22 of the present invention. Table 22 belowlists the various data explained above for Embodiment 22.

The object-side surface of the first lens component of Embodiment 22 isan aspheric surface expressed by the following equation:

$\begin{matrix}{Z = {\frac{Y^{2}R}{1 + \left\{ {1 - {\left( {K + 1} \right) \cdot \left( {Y/R} \right)^{2}}} \right\}^{{- 1}/2}} + {\sum\limits_{n = 2}^{10}\left( {A_{2\; n} \cdot Y^{2\; n}} \right)}}} & {{Equation}\mspace{14mu}(A)}\end{matrix}$where

Z is the length (in mm) of a line drawn from a point on the asphericlens surface at a distance Y from the optical axis to the tangentialplane of the aspheric surface vertex,

R is the radius of curvature (in mm) of the aspheric lens surface on theoptical axis,

Y is the distance (in mm) from the optical axis,

K is the eccentricity, and

A_(2n) is the ith aspheric coefficient and the summation extends over 2nfrom n equals two to ten.

In Embodiment 22 of the present invention, only aspheric coefficientsA₄, A₆, and A₈ are non-zero. These non-zero values and other valuesrelated to Equation (A) above with regard to the lens surface withradius of curvature r₃ above are shown in the middle of Table 22 below.

TABLE 22 Far point focused state WD = 48 f_(TF) = 1.804 F_(NO) = 4.48 2ω = 82.0° Near point focused state WD = 22.5 f_(TN) = 1.764 F_(NO) =4.40 2 ω = 83.4° r₁ = ∞ d₁ = 0.4000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ =0.5000 r₃ = 100 (aspheric) d₃ = 0.5000 n₂ = 1.80610 ν₂ = 40.88 r₄ =1.6055 d₄ = 0.6500 r₅ = ∞ d₅ = 5.5000 n₃ = 1.88300 ν₃ = 40.76 r₆ = ∞(stop) d₆ = 0.4000 r₇ = 8.6334 d₇ = 0.5000 n₄ = 1.88300 ν₄ = 40.76 r₈ =−8.6334 d₈ = 0.6347 r₉ = 6.1623 d₉ = 0.6000 n₅ = 1.80100 ν₅ = 34.97 r₁₀= −10.9223 d₁₀ = 0.3398 r₁₁ = −5.3215 d₁₁ = 0.3000 n₆ = 1.88300 ν₆ =40.76 r₁₂ = 3.8000 d₁₂ = 0.8500 n₇ = 1.48749 ν₇ = 70.23 r₁₃ = −3.4079d₁₃ = 0.1230 r₁₄ = 50.0407 d₁₄ = 0.3000 n₈ = 1.88300 ν₈ = 40.76 r₁₅ =2.9659 d₁₅ = 1.0500 n₉ = 1.48749 ν₉ = 70.23 r₁₆ = −3.8154 d₁₆ = 0.1000r₁₇ = 7.9926 d₁₇ = 0.9500 n₁₀ = 1.48749 ν₁₀ = 70.23 r₁₈ = −2.6500 d₁₈ =0.3000 n₁₁ = 1.84666 ν₁₁ = 23.78 r₁₉ = −5.6345 d₁₉ = 0.1000 r₂₀ = ∞ d₂₀= 0.4500 n₁₂ = 1.51800 ν₁₂ = 75.00 r₂₁ = ∞ d₂₁ = 0.6000 r₂₂ = ∞ d₂₂ =3.6000 n₁₃ = 1.48749 ν₁₃ = 70.23 r₂₃ = ∞ (image plane) R = r₃ = 100 K =0 A₄ = 1.8935 × 10⁻² A₆ = −3.9808 × 10⁻³ A₈ = 5.5246 × 10⁻⁴|f_(UM)/f_(TF)| = 2.747 f_(U1)/f_(TF) = −1.125 f_(TN)/f_(TF) = 0.978f_(U1) = −2.029 f_(U1)/f_(TF) = −1.13 f_(U2) = 4.956 f_(U2)/f_(TF) =2.75 f_(U3) = 4.996 f_(U3)/f_(TF) = 2.77 f_(U4) = −9.649 f_(U4)/f_(TF) =−5.35 f_(U5) = 44.483 f_(U5)/f_(TF) = 24.66 f_(UR) = 13.015f_(UR)/f_(TF) = 7.22 |f_(U) (GM, GR)|_(min) = 2.75 |R (GM, GR)|_(min) =1.47 n(GR_(p)) = n₁₀ = 1.48749 n(GR_(n)) = n₁₁ = 1.84666 ν(GR_(p)) = ν₁₀= 70.23 ν(GR_(n)) = ν₁₁ = 23.78

As shown in FIG. 22, the optical system of Embodiment 22 is composed of:a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₃ and r₄; a middle lens groupthat is composed of four lens components, specifically, second and thirdlens components that have positive refractive power and are each formedof a single lens element with lens surfaces having radii of curvature(r₇ and r₈) and (r₉ and r₁₀) respectively, and cemented fourth and fifthlens components, each of which is formed of a biconcave lens elementcemented to a biconvex lens element and having radii of curvature (r₁₁,r₁₂ and r₁₃) and (r₁₄, r₁₅ and r₁₆), respectively; and a rear lens groupcomposed of a cemented lens component formed of a biconvex lens elementcemented to a meniscus lens element having negative refractive powerwith radii of curvature r₁₇, r₁₈, and r₁₉.

Embodiment 22 is an example of an optical system according to the firstand third modes of construction of the present invention with the middlelens group, referenced by “GM” in Table 22 above and in FIG. 22, beingcomposed of the second lens component having positive refractive power,third and fourth lens components, and the fifth lens component havingpositive refractive power.

Embodiment 22 is designed for use in a videoscope that includes anoblique view. Therefore, Embodiment 22 has a narrower field of view thanin Embodiments 1-21. However, astigmatism is reduced by using anaspheric surface at the object-side surface with radius of curvature r₃of the first lens component so that it embodies an optical system with afocal length that is nearly the same as in Embodiments 1-21, describedabove.

In Embodiment 22, a stop S for controlling image brightness and having aradius of curvature r₆ is arranged between the first lens component andthe second lens component, and a glass block B2 having radii ofcurvature r₅ and r₆ and having a long glass length is arranged betweenthe first lens component and the stop S. Additionally, Embodiment 22 canbe made into an objective optical system with an oblique view bychanging this glass block into an oblique viewing prism.

In Embodiment 22, when it is used in a videoscope with an oblique view,for example, a videoscope being used in endoscope surgery, a rotatingmechanism for rotating a monitor picture in the direction of observationfor the convenience of visual field viewing becomes necessary.

In Embodiment 22, the objective optical system is divided between thesecond lens component and the third lens component as shown in FIG. 22so as to define on the object side a fixed lens group G_(fix) and on theimage side a rotational lens group Got, as indicated by brackets at thebottom of FIG. 22. The fixed lens group G_(fix) is fixed in an insertionpart, and the rotational lens group G_(rot) is constructed so as to berotatable in the insertion part. In this case, the rotation of themonitor picture is made possible only by rotating a solid-state imagepickup element, but this is undesirable because image quality problems,such as focus deviation, occur during rotation. Moreover, the divisionof the fixed lens group G_(fix) and the rotational lens group G_(rot) ata position where the light in the light path is nearly a focal, asillustrated, is desirable.

In Embodiment 22, the second lens component that is on the image sideend of the fixed lens group G_(fix) and that is in the middle group isused as the lens component that is moved for focusing, and an actuatorfor moving this lens component is fixed and arranged in the insertionpart.

Embodiment 22 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 22 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them. In Embodiment 22, theimage side lens component that forms the rear lens group is a cementedlens component composed of a lens element having positive refractivepower cemented to a lens element having negative refractive power, and,as described above, the refractive indices n(GR_(p)) and n(GR_(n)) andthe Abbe numbers v(GR_(p)) and v(GR_(n)) of the lens materials of thecemented lens component that is the last lens component satisfy theapplicable conditions and design criteria of the present invention.

FIGS. 49A-49C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 22 of the present invention whenfocused at the far point on the object side, and FIGS. 49D-49F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 22 of the present invention when focused at the near point onthe object side. As shown in FIGS. 49A-49C and FIGS. 49D-49F, inEmbodiment 22 these aberrations are favorably corrected.

EMBODIMENT 23

FIG. 23 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 23 of the present invention. Table 23 belowlists the various data explained above for Embodiment 23.

The object-side surface of the first lens component of Embodiment 23 isan aspheric surface expressed by Equation (A) described above withregard to Embodiment 22. In Embodiment 23 of the present invention, onlyaspheric coefficients A₄, A₆, and A₈ are non-zero. These non-zero valuesand other values related to Equation (A) above with regard to the lenssurface with radius of curvature r₃ are shown in the middle of Table 23below.

TABLE 23 Far point focused state WD = 48 f_(TF) = 1.804 F_(NO) = 4.48 2ω = 82.0° Near point focused state WD = 22.5 f_(TN) = 1.808 F_(NO) =4.51 2 ω = 81.4° r₁ = ∞ d₁ = 0.4000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ =0.5000 r₃ = 100 (aspheric) d₃ = 0.5000 n₂ = 1.80610 ν₂ = 40.88 r₄ =1.6090 d₄ = 0.6500 r₅ = ∞ d₅ = 5.5000 n₃ = 1.88300 ν₃ = 40.76 r₆ = ∞(stop) d₆ = 0.2000 r₇ = 9.7009 d₇ = 0.5000 n₄ = 1.88300 ν₄ = 40.76 r₈ =−9.7009 d₈ = 0.1000 r₉ = 9.0734 d₉ = 0.6000 n₅ = 1.80100 ν₅ = 34.97 r₁₀= −8.8591 d₁₀ = 0.4834 r₁₁ = −5.8965 d₁₁ = 0.3000 n₆ = 1.88300 ν₆ =40.76 r₁₂ = 4.1000 d₁₂ = 0.8500 n₇ = 1.48749 ν₇ = 70.23 r₁₃ = −3.2639d₁₃ = 0.6026 r₁₄ = −241.5149 d₁₄ = 0.3000 n₈ = 1.88300 ν₈ = 40.76 r₁₅ =3.0356 d₁₅ = 1.0500 n₉ = 1.58913 ν₉ = 61.14 r₁₆ = −3.6847 d₁₆ = 0.1000r₁₇ = 9.8915 d₁₇ = 0.9500 n₁₀ = 1.48749 ν₁₀ = 70.23 r₁₈ = −2.6760 d₁₈ =0.3000 n₁₁ = 1.84666 ν₁₁ = 23.78 r₁₉ = −5.9533 d₁₉ = 0.1000 r₂₀ = ∞ d₂₀= 0.4500 n₁₂ = 1.51800 ν₁₂ = 75.00 r₂₁ = ∞ d₂₁ = 0.6000 r₂₂ = ∞ d₂₂ =3.6000 n₁₃ = 1.48749 ν₁₃ = 70.23 r₂₃ = ∞ (image plane) R = r₃ = 100 K =0 A₄ = 1.9065 × 10⁻² A₆ = −4.2103 × 10⁻³ A₈ = 6.1429 × 10⁻⁴|f_(UM)/f_(TF)| = 7.452 f_(U1)/f_(TF) = −1.127 f_(TN)/f_(TF) = 1.002f_(U1) = −2.033 f_(U1)/f_(TF) = −1.13 f_(U2) = 5.560 f_(U2)/f_(TF) =3.08 f_(U3) = 5.681 f_(U3)/f_(TF) = 3.15 f_(U4) = −13.443 f_(U4)/f_(TF)= −7.45 f_(U5) = 14.270 f_(U5)/f_(TF) = 7.91 f_(UR) = 16.980f_(UR)/f_(TF) = 9.41 |f_(U) (GM, GR)|_(min) = 3.08 |R (GM, GR)|_(min) =1.48 n(GR_(p)) = n₁₀ = 1.48749 n(GR_(n)) = n₁₁ = 1.84666 ν(GR_(p)) = ν₁₀= 70.23 ν(GR_(n)) = ν₁₁ = 23.78

Embodiment 23 is designed for use in a videoscope that includes anoblique view, similar to Embodiment 22 described above.

Embodiment 23 is an example of an optical system according to the firstand third modes of construction of the present invention with the middlelens group, referenced by “GM” in Table 23 above and in FIG. 23, beingcomposed of the second lens component having positive refractive power,third and fourth lens components, and the fifth lens component being acemented lens component having positive refractive power.

Embodiment 23 is different from Embodiment 22 in that in Embodiment 23the fourth lens component is moved for focusing, and that movement istoward the image side.

When the objective optical system of Embodiment 23 is used for obliqueviewing and divided into a fixed lens group G_(fix) that is fixed in theinsertion part of the endoscope and a rotational lens group G_(rot), theoptical system is divided between the fourth lens component and thefifth lens component, as illustrated in FIG. 23, with the fixed lensgroup G_(fix) on the object side and the rotational lens group G_(rot)on the image side, as indicated by brackets at the bottom of FIG. 23.Then, an image can be rotated by rotating the rotational group G_(rot)around the insertion part. The fourth lens component is the lenscomponent that is moved for focusing and, as in Embodiment 22, it formspart of the fixed lens group G_(fix). Therefore, an actuator for movingthe focusing lens component is fixed and arranged in the insertion part.

Embodiment 23 of the present invention satisfies Conditions (1) through(7) above, as shown by Table 23 above. The focal lengths f_(U)(GM,GR) ofthe lens components in the middle lens group and rear lens group and theradii of curvature R(GM,GR) of the lens surfaces of the lens componentsin the middle lens group and rear lens group also satisfy the applicableconditions and design criteria specified for them. In Embodiment 23, theimage side lens component that forms the rear lens group is a cementedlens component composed of a lens element having positive refractivepower cemented to a lens element having negative refractive power, and,as described above, the refractive indices n(GR_(p)) and n(GR_(n)) andthe Abbe numbers v(GR_(p)) and v(GR_(n)) of the lens materials of thecemented lens component that is the last lens component satisfy theapplicable conditions and design criteria of the present invention.

FIGS. 50A-50C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 23 of the present invention whenfocused at the far point on the object side, and FIGS. 50D-50F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 23 of the present invention when focused at the near point onthe object side. As shown in FIGS. 50A-50C and FIGS. 50D-50F, inEmbodiment 23 these aberrations are favorably corrected.

EMBODIMENT 24

FIG. 24 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 24 of the present invention. Table 24 belowlists the various data explained above for Embodiment 24.

TABLE 24 Far point focused state WD = 46 f_(TF) = 1.900 F_(NO) = 4.51 2ω = 98.6° Near point focused state WD = 23 f_(TN) = 1.898 F_(NO) = 4.512 ω = 97.2° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.3668 d₂ =0.6677 r₃ = 3.0512 d₃ = 0.8469 n₂ = 1.59270 ν₂ = 35.31 r₄ = 4.1365 d₄ =0.7515 r₅ = ∞ (stop) d₅ = 0.4801 r₆ = −35.9069 d₆ = 0.7000 n₃ = 1.77250ν₃ = 49.60 r₇ = −2.3945 d₇ = 1.6607 r₈ = 12.3406 d₈ = 1.3500 n₄ =1.71999 ν₄ = 50.23 r₉ = −2.1108 d₉ = 0.3000 n₅ = 1.92286 ν₅ = 18.90 r₁₀= −4.3910 d₁₀ = 0.1000 r₁₁ = ∞ d₁₁ = 0.4500 n₆ = 1.51800 ν₆ = 75.00 r₁₂= ∞ d₁₂ = 0.6000 r₁₃ = ∞ d₁₃ = 3.6000 n₇ = 1.48749 ν₇ = 70.23 r₁₄ = ∞(image plane) |f_(UM)/f_(TF)| = 8.003 f_(U1)/f_(TF) = −0.936f_(TN)/f_(TF) = 0.999 f_(U1) = −1.779 f_(U1)/f_(TF) = −0.94 f_(U2) =15.206 f_(U2)/f_(TF) = 8.00 f_(U3) = 3.291 f_(U3)/f_(TF) = 1.73 f_(UR) =5.943 f_(UR)/f_(TF) = 3.13 |f_(U) (GM, GR)|_(min) = 1.73 |R (GM,GR)|_(min) = 1.11 n(GR_(p)) = n₄ = 1.71999 n(GR_(n)) = n₅ = 1.92286ν(GR_(p)) = ν₄ = 50.23 ν(GR_(n)) = ν₅ = 18.90

The optical system of Embodiment 24, as shown in FIG. 24, is composedof: a front lens group that consists of a first lens component that hasnegative refractive power and is formed of a single lens element withlens surfaces having radii of curvature r₁ and r₂; a middle lens groupthat is composed of two lens components, specifically, second and thirdlens components that have positive refractive power and are each formedof a single lens element with lens surfaces having radii of curvature(r₃ and r₄) and (r₆ and r₇), respectively; and a rear lens groupcomposed of a fourth cemented lens component formed of a biconvex lenselement cemented to a meniscus lens element having negative refractivepower with radii of curvature r₈, r₉ and r₁₀. A stop S for controllingimage brightness and having a radius of curvature r₅ is arranged betweenthe second lens component and the third lens component in the middlelens group at a position providing a lower ray height. In Embodiment 24,the second lens component is the lens component that moves for focusingand it moves toward the image side during focusing from the far point tothe near point.

Embodiment 24 is an example of an optical system according to the fourthmode of construction of the present invention described above withregard to the middle lens group, referenced by “GM” in Table 24 aboveand in FIG. 24, and is composed of second and third lens components,each of which is formed as a single lens element.

The fourth or rear lens component is formed as a cemented lens componentin order to correct astigmatism and lateral color.

Embodiment 24 has a longer far point focal length f_(TF) thanEmbodiments 1-23 above, and has relatively large astigmatism resultingin unfavorable depth of field, but operates satisfactorily when in use.

Embodiment 24 of the present invention satisfies Conditions (1) through(7) above. The focal lengths f_(U)(GM,GR) of the lens components in themiddle lens group and rear lens group and the radii of curvatureR(GM,GR) of the lens surfaces of the lens components in the middle lensgroup and rear lens group also satisfy the applicable conditions anddesign criteria specified for them. As described above, the refractiveindices n(GR_(p)) and n(GR_(n)) and the Abbe numbers v(GR_(p)) andv(GR_(n)) of the lens materials of the cemented lens component that isthe last lens component also satisfy the applicable conditions anddesign criteria of the present invention.

FIGS. 51A-51C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 24 of the present invention whenfocused at the far point on the object side, and FIGS. 51D-51F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 24 of the present invention when focused at the near point onthe object side. As shown in FIGS. 51A-51C and FIGS. 51D-51F, inEmbodiment 24 these aberrations are favorably corrected.

EMBODIMENT 25

FIG. 25 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 25 of the present invention. Table 25 belowlists the various data explained above for Embodiment 25.

TABLE 25 Far point focused state WD = 46 f_(TF) = 1.900 F_(NO) = 4.51 2ω = 98.6° Near point focused state WD = 23 f_(TN) = 1.833 F_(NO) = 4.372 ω = 102.6° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.3870 d₂ =0.5500 r₃ = 29.8167 d₃ = 0.8000 n₂ = 1.74077 ν₂ = 27.79 r₄ = −11.0393 d₄= 0.8931 r₅ = ∞ (stop) d₅ = 0.7281 r₆ = −6.1867 d₆ = 0.7000 n₃ = 1.72916ν₃ = 54.68 r₇ = −2.2463 d₇ = 1.1458 r₈ = 5.2651 d₈ = 1.3000 n₄ = 1.58913ν₄ = 61.14 r₉ = −2.4546 d₉ = 0.3000 n₅ = 1.92286 ν₅ = 18.90 r₁₀ =−4.5363 d₁₀ = 0.1000 r₁₁ = ∞ d₁₁ = 0.4500 n₆ = 1.51800 ν₆ = 75.00 r₁₂ =∞ d₁₂ = 1.0729 r₁₃ = ∞ d₁₃ = 3.6000 n₇ = 1.48749 ν₇ = 70.23 r₁₄ = ∞(image plane) |f_(UM)/f_(TF)| = 2.368 f_(U1)/f_(TF) = −0.951f_(TN)/f_(TF) = 0.965 f_(U1) = −1.806 f_(U1)/f_(TF) = −0.95 f_(U2) =10.967 f_(U2)/f_(TF) = 5.77 f_(U3) = 4.500 f_(U3)/f_(TF) = 2.37 f_(UR) =5.762 f_(UR)/f_(TF) = 3.03 |f_(U) (GM, GR)|_(min) = 2.37 |R (GM,GR)|_(min) = 1.18 n(GR_(p)) = n₄ = 1.58913 n(GR_(n)) = n₅ = 1.92286ν(GR_(p)) = ν₄ = 61.14 ν(GR_(n)) = ν₅ = 18.90

Embodiment 25 is an optical system that is similar to Embodiment 24, butin Embodiment 25 the lens component that moves for focusing is the thirdlens component and it moves toward the image side during focusing fromthe far point to the near point. Thus, Embodiment 25 is also, as withEmbodiment 24, an example of an optical system according to the fourthmode of construction of the present invention described above.

Embodiment 25 of the present invention satisfies Conditions (1) through(7) above. The focal lengths f_(U)(GM,GR) of the lens components in themiddle lens group and rear lens group and the radii of curvatureR(GM,GR) of the lens surfaces of the lens components in the middle lensgroup and rear lens group also satisfy the applicable conditions anddesign criteria specified for them. As described above, the refractiveindices n(GR_(p)) and n(GR_(n)) and the Abbe numbers v(GR_(p)) andv(GR_(n)) of the lens materials of the cemented lens component that isthe last lens component also satisfy the applicable conditions anddesign criteria of the present invention.

FIGS. 52A-52C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 25 of the present invention whenfocused at the far point on the object side, and FIGS. 52D-52F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 25 of the present invention when focused at the near point onthe object side. As shown in FIGS. 52A-52C and FIGS. 52D-52F, inEmbodiment 25 these aberrations are favorably corrected.

EMBODIMENT 26

FIG. 26 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 26 of the present invention. Table 26 belowlists the various data explained above for Embodiment 26.

TABLE 26 Far point focused state WD = 46 f_(TF) = 1.939 F_(NO) = 4.50 2ω = 98.6° Near point focused state WD = 23 f_(TN) = 1.858 F_(NO) = 4.342 ω = 103.3° r₁ = ∞ d₁ = 0.5000 n₁ = 1.76820 ν₁ = 71.79 r₂ = 1.4602 d₂ =0.5500 r₃ = 3.9082 d₃ = 0.8000 n₂ = 1.92286 ν₂ = 18.90 r₄ = 9.8536 d₄ =0.6318 r₅ = ∞ (stop) d₅ = 0.7290 r₆ = −9.6808 d₆ = 0.3000 n₃ = 1.92286ν₃ = 18.90 r₇ = 4.2583 d₇ = 0.8500 n₄ = 1.72916 ν₄ = 54.68 r₈ = −2.3985d₈ = 0.5502 r₉ = 5.5309 d₉ = 0.6906 n₅ = 1.72916 ν₅ = 54.68 r₁₀ =−9.4912 d₁₀ = 0.1000 r₁₁ = ∞ d₁₁ = 0.4500 n₆ = 1.51800 ν₆ = 75.00 r₁₂ =∞ d₁₂ = 1.2697 r₁₃ = ∞ d₁₃ = 3.6000 n₇ = 1.48749 ν₇ = 70.23 r₁₄ = ∞(image plane) |f_(UM)/f_(TF)| = 2.741 f_(U1)/f_(TF) = −0.980f_(TN)/f_(TF) = 0.958 f_(U1) = −1.901 f_(U1)/f_(TF) = −0.98 f_(U2) =6.593 f_(U2)/f_(TF) = 3.40 f_(U3) = 5.314 f_(U3)/f_(TF) = 2.74 f_(UR) =4.887 f_(UR)/f_(TF) = 2.52 |f_(U) (GM, GR)|_(min) = 2.52 |R (GM,GR)|_(min) = 1.24

As shown in FIG. 26, Embodiment 26 is an optical system that is similarto Embodiment 25, but in Embodiment 26 the third lens component thatmoves for focusing is composed of a biconcave lens element cemented to abiconvex lens element while, on the other hand, the last or rear lenscomponent that forms the rear lens group is a single lens element. Thus,Embodiment 26 is an example of an optical system according to the fourthmode of construction of the present invention described above.

Embodiment 26 of the present invention satisfies Conditions (1) through(7) above. The focal lengths f_(U)(GM,GR) of the lens components in themiddle lens group and rear lens group and the radii of curvatureR(GM,GR) of the lens surfaces of the lens components in the middle lensgroup and rear lens group also satisfy the applicable conditions anddesign criteria specified for them.

FIGS. 53A-53C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 26 of the present invention whenfocused at the far point on the object side, and FIGS. 53D-53F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 26 of the present invention when focused at the near point onthe object side. As shown in FIGS. 53A-53C and FIGS. 53D-53F, inEmbodiment 26 these aberrations are favorably corrected.

EMBODIMENT 27

FIG. 27 shows a cross-sectional view of the objective optical system foran endoscope of Embodiment 27 of the present invention. Table 27 belowlists the various data explained above for Embodiment 27.

TABLE 27 Far point focused state WD = 46 f_(TF) = 1.931 F_(NO) = 4.45 2ω = 98.6° Near point focused state WD = 23 f_(TN) = 1.863 F_(NO) = 4.322 ω = 102.5° r₁ = ∞ d₁ = 0.7000 n₁ = 1.76820 ν₁ = 71.79 r₂ = ∞ d₂ =0.2900 r₃ = ∞ d₃ = 0.3000 n₂ = 1.88300 ν₂ = 40.76 r₄ = 1.3698 d₄ =0.5500 r₅ = 2.7509 d₅ = 1.0923 n₃ = 1.92286 ν₃ = 18.90 r₆ = 6.0400 d₆ =0.0913 r₇ = ∞ (stop) d₇ = 0.4068 r₈ = −5.9929 d₈ = 0.3000 n₄ = 1.88300ν₄ = 40.76 r₉ = 3.8118 d₉ = 0.9500 n₅ = 1.72916 ν₅ = 54.68 r₁₀ = −2.0854d₁₀ = 0.5046 r₁₁ = 5.7672 d₁₁ = 1.2000 n₆ = 1.72916 ν₆ = 54.68 r₁₂ =−2.7668 d₁₂ = 0.3000 n₇ = 1.92286 ν₇ = 18.90 r₁₃ = −5.0472 d₁₃ = 0.1000r₁₄ = ∞ d₁₄ = 0.4500 n₈ = 1.51800 ν₈ = 75.00 r₁₅ = ∞ d₁₅ = 0.9776 r₁₆ =∞ d₁₆ = 3.6000 n₉ = 1.48749 ν₉ = 70.23 r₁₇ = ∞ (image plane)|f_(UM)/f_(TF)| = 2.521 f_(U1)/f_(TF) = −0.803 f_(TN)/f_(TF) = 0.965f_(U1) = −1.551 f_(U1)/f_(TF) = −0.80 f_(U2) = 4.721 f_(U2)/f_(TF) =2.44 f_(U3) = 4.868 f_(U3)/f_(TF) = 2.52 f_(UR) = 4.394 f_(UR)/f_(TF) =2.28 |f_(U) (GM, GR)|_(min) = 2.28 |R (GM, GR)|_(min) = 1.08 n(GR_(p)) =n₆ = 1.72916 n(GR_(n)) = n₇ = 1.92286 ν(GR_(p)) = ν₆ = 54.68 ν(GR_(n)) =ν₇ = 18.90

As shown in FIG. 27, Embodiment 27 is an optical system that is similarto Embodiment 25 shown in FIG. 25, but with the third lens component inEmbodiment 27 being a cemented lens component. Thus, Embodiment 27 is anexample of an optical system according to the fourth mode ofconstruction of the present invention described above.

Embodiment 27 of the present invention satisfies Conditions (1) through(7) above. The focal lengths f_(U)(GM,GR) of the lens components in themiddle lens group and rear lens group and the radii of curvatureR(GM,GR) of the lens surfaces of the lens components in the middle lensgroup and rear lens group also satisfy the applicable conditions anddesign criteria specified for them. As described above, the refractiveindices n(GR_(p)) and n(GR_(n)) and the Abbe numbers v(GR_(p)) andv(GR_(n)) of the lens materials of the cemented lens component that isthe last lens component also satisfy the applicable conditions anddesign criteria of the present invention.

FIGS. 54A-54C show the spherical aberration, astigmatism, anddistortion, respectively, of Embodiment 27 of the present invention whenfocused at the far point on the object side, and FIGS. 54D-54F show thespherical aberration, astigmatism, and distortion, respectively, ofEmbodiment 27 of the present invention when focused at the near point onthe object side. As shown in FIGS. 54A-54C and FIGS. 54D-54F, inEmbodiment 27 these aberrations are favorably corrected.

All of Embodiments 1-27 above may be used with image pickup elementshaving a pixel pitch of 2.1 μm arranged on the image plane. The maximumimage height is 1.469 mm, and the f-number is about 4.5. When a coverglass C is arranged on the object-most side it is made of sapphire. Whena cover glass is not used, sapphire is used as the material for theobject-most side lens element. An absorption type infrared cutoff filterF is arranged in the optical system, and a prism for horizontallyplacing the image pickup elements and/or a glass block B representing amultiplate prism unit are arranged on the image-most side.

The objective optical system for an endoscope of the present inventionis suited to a high-precision endoscope having a focusing functionperformed by movement of a lens component, and it is an optical systemin which the lens component that moves for focusing is small,aberrations are favorably corrected and fluctuate little with focusingmovement of the focusing lens component.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention. Rather, the scopeof the invention shall be defined as set forth in the following claimsand their legal equivalents. All such modifications as would be obviousto one skilled in the art are intended to be included within the scopeof the following claims.

1. An objective optical system for an endoscope having an object sideand an image side and comprising, arranged along an optical axis inorder from the object side, as follows: a front lens group havingnegative refractive power and consisting of a first lens component; amiddle lens group having positive refractive power and including atleast two lens components, each of said at least two lens componentshaving positive refractive power; and a rear lens group having positiverefractive power and consisting of one lens component; wherein only onelens component of said middle lens group moves in the direction of theoptical axis during focusing; a stop for controlling image brightness ispositioned within said middle lens group or between said front lensgroup and said middle lens group; and the following conditions aresatisfied:2<|f _(UM) /f _(TF)|<10−1.25<f _(U1) /f _(TF)<−0.6 where f_(UM) is the focal length of saidonly one lens component; f_(TF) is the focal length of the entireobjective optical system for an endoscope focused at the far point onthe object side; and f_(U1) is the focal length of said first lenscomponent.
 2. The objective optical system for an endoscope of claim 1,wherein said middle lens group is formed of at least three lenscomponents.
 3. The objective optical system for an endoscope of claim 2,wherein said middle lens group consists of, arranged in the followingorder from the object side, a second lens component having positiverefractive power, a third lens component, and a fourth lens componenthaving positive refractive power.
 4. The objective optical system for anendoscope of claim 2, wherein said middle lens group consists of,arranged in the following order from the object side, a second lenscomponent having positive refractive power, a third lens component, afourth lens component having positive refractive power, and a fifth lenscomponent having positive refractive power.
 5. The objective opticalsystem for an endoscope of claim 1, wherein said middle lens groupconsists of, arranged in the following order from the object side, asecond lens component having positive refractive power, said stop, and athird lens component having positive refractive power.
 6. The objectiveoptical system for an endoscope of claim 1, wherein the followingcondition is satisfied:0.85<f _(TN) /f _(TF)<1.15 where f_(TN) is the focal length of theentire objective optical system for an endoscope focused at the nearpoint on the object side.
 7. The objective optical system for anendoscope of claim 1, wherein the following condition is satisfied:0.85<f _(TN) /f _(TF)<1 where f_(TN) is the focal length of the entireobjective optical system for an endoscope focused at the near point onthe object side.
 8. The objective optical system for an endoscope ofclaim 1, wherein the following conditions are satisfied:n_(U1)>1.7v_(U1)>38 where n_(U1) is the refractive index at the d-line of saidfirst lens component; and v_(U1) is the Abbe number at the d-line ofsaid first lens component.
 9. The objective optical system for anendoscope of claim 1, wherein said first lens component consists of aplano-concave lens element formed of sapphire material.
 10. Theobjective optical system for an endoscope of claim 1, wherein thefollowing condition is satisfied:|f _(U)(GM,GR)|≧1.4f _(TF) where f_(U)(GM,GR) is the focal length ofeach of the lens components of each of said middle lens group and ofsaid rear lens group.
 11. The objective optical system for an endoscopeof claim 1, wherein the following condition is satisfied:|R(GM,GR)|>0.8f _(TF) where R(GM,GR) is the radius of curvature of eachlens surface of each lens element of each of the lens components of eachof said middle lens group and of said rear lens group.
 12. The objectiveoptical system for an endoscope of claim 1, wherein said rear lens groupconsists of a cemented lens component formed of a lens element havingnegative refractive power and a lens element having positive refractivepower that satisfy the following conditions:n(GR _(n))>1.82v(GR _(n))<26n(GR _(p))<1.78v(GR _(p))>49 where n(GR_(n)) is the refractive index at the d-line ofsaid lens element having negative refractive power; v(GR_(n)) is theAbbe number at the d-line of said lens element having negativerefractive power; n(GR_(p)) is the refractive index at the d-line ofsaid lens element having positive refractive power; and v(GR_(p)) is theAbbe number at the d-line of said lens element having positiverefractive power.
 13. The objective optical system for an endoscope ofclaim 1, wherein the following condition is satisfied:2<f _(UR) /f _(TF)<12 where f_(UR) is the focal length of the lenscomponent of said rear lens group.
 14. The objective optical system foran endoscope of claim 1, wherein each of at least two lens componentsconsists of a lens element having negative refractive power that iscemented to a lens element having positive refractive power and having arefractive index that is at least 0.1 less than the refractive index ofsaid lens element having negative refractive power.
 15. The objectiveoptical system for an endoscope of claim 1, wherein said only one lenscomponent consists of a single lens element having positive refractivepower and a refractive index of 1.75 or less.
 16. The objective opticalsystem for an endoscope of claim 1, wherein said only one lens componenthas positive refractive power and consists of a lens element havingnegative refractive power and a lens element having positive refractivepower, with the lens element having positive refractive power having arefractive index that is at least 0.1 less than the refractive index ofsaid lens element having negative refractive power.
 17. The objectiveoptical system for an endoscope of claim 1, wherein said only one lenscomponent is adjacent said stop.
 18. The objective optical system for anendoscope of claim 1, wherein the one lens component of the middle lensgroup that moves in the direction of the optical axis during focusing isother than the object-side lens component or the image-side lenscomponent of said middle lens group.
 19. The objective optical systemfor an endoscope of claim 1, wherein each of the object-side lenscomponent of said middle lens group and the image-side lens component ofsaid middle lens group has positive refractive power.